I devised this build probably sometime in 6.x, when standard snipery things like Desolator and Malestrom were Unique Attack Modifiers and couldn't both go off at the same time. I desired something that was efficient with early-game money, because Sniper is more dependent on items than most, so I focused on buying things I knew I'd require later.
Most of the time I'm playing this build center lane with friends & family vs bots. They're usually the DOTA experts, I required an easy way to navigate the game and stay relevant without getting lost in all the shop options. I don't pretend that this build is going to work in pro settings and it will probably generate a lot of criticism, which I'm open to hearing in service of learning the game.
I just yesterday found out that in 7.0-7.2, A's Scepter upgrades Sniper's ult, and Desolator and Malestrom are no longer Unique Attack Modifiers. So that changes the foundational aspects of Sniper meta, and I desire to explore those in other builds. But first, I desire to document something that has brought me a lot of success, at least vs bots.
Sniper is a carry, and he takes a long time to develop. He starts out slow and squishy with abysmal attack and moderately slow attack speed. Expecting a lot out of him before level ~8 is a recipe for disappointment and a lot of early deaths, and he doesn't become really fun to play unless you're either four levels ahead of everyone on the other team or about level 18 or so while fairly even. This is an endgame character, and everything from the beginning of the game until then is balancing disaster management (i.e. not dying) with farming gold.
One way I came up with to address the gold problem was to spend my early gold on items that directly impacted the early game, and were still relevant during and after the midgame. No Iron Branches for me! So early game purchases are on items that directly improve attack speed and damage and are components of midgame items.
Another way was to start with a Headshot first skill build. The extra damage noticeably widens that last-hit window of health enemy creeps have, and I've gotten pretty reliable with it particularly after level 3. Blades of Attack helps even more.
Many sniper builds I'm seeing focus on developing range (Take Aim) or Shrapnel. I struggled, particularly < 5, in my range-first to get those last hits - either I waited too long and the enemy creep dies, or I shoot too soon and the creep survives my shot - which means either the enemy hero gets a deny, or my own creep kills it! One day it dawned on me that one of my own abilities increases my damage potential - Headshot - and that I really wasn't using the range of Take Aim until later in the game anyway. So I started going with Headshot first builds, and my early game last hit numbers started going up.
This is not to say that you shouldn't adjust in situations where it's warranted. If you're up against a ranged enemy hero in your lane, a little more distance can be comforting, as you don't have a lot of health to spare. I like Headshot at 5 because it helps farm gold faster, and you really aren't going to be seeking hero engagements until much later anyway. If I'm feeling risky and the situation allows, I'll even take Headshot again at level 7, but often it makes more sense to have the 2nd Take Aim around that point unless enemy heroes are determined to leave you alone, in which case you should punish them for it by raking in gold that much faster.
I also like to take one level of Shrapnel before level 4. If you don't take it at level 2 or 4, you're not going to have an opportunity to do so until much later, and it's particularly useful in a lot of situations - less often for direct damage than for its slow effect on enemies, which is both useful on the chase as well as when retreating because most heroes are faster than you.
You'll notice that this build does not focus on many early game items that you'd typically expect a character to have. This is intentional, and it has two purposes: eliminate wasting gold (which Sniper is highly dependent on) and get those last hits!
Gloves of Haste increase attack speed so that if you shoot too early, you're able to queue up another shot more quickly. With a eadshot-first build, the amount of health a creep has left before you can one-shot it varies because the Headshot has a 40% chance to go off, and the damage difference can be enough that the creep survives your hit, survives one of your creep's hits, and is still alive for you to que up a second shot and rake in that gold. It'll work less against a vigilant enemy hero in your lane, but it can still be worth it if they're distracted by something else (i.e. their own farming). Without the gloves, queuing up that 2nd shot takes an eternity.
Blades of Attack are immensely awesome bang for the buck and I like to get them early. At level 1 it's almost a 25% boost to your damage output! I used to buy them first, when I was making range-first builds, and they're still useful enough to buy them before boots if you play with enough awareness not to get gangked (that's what the ward is for!), even if I don't make the Crysalis until after Power Treads and an escape.
After the Blades, I go for Power Treads. The agility, attack speed and movement bonus are particularly good bang for the buck, and now this guy starts to have enough damage output to farm in earnest. You no longer have to follow your creeps' damage lead; you can 3-shot the ranged creep, mop up the melee creeps, and push the tower with 2 or 3 healthy friendly creeps pretty reliably. This is where the ward comes in, particularly if you're in center lane (if you're on the side lanes, your support should be doing this for you).
Power Treads and enough damage output to start to make a difference on the field usually converge about level 8, and you know that once this happens, you're going to become a target. If you didn't have to worry about escaping, I'd skip shadow blade and go straight for either damage (Chrysalis) or staying power (lifesteal via shadow mask). However, you're no good to your team dead, and it costs you gold to die. That's bad. So it's worth spending some gold on an escape. Shadow Blade is a good one that also boosts your stats. It's a little expensive for this part of the game, but the benefits outweigh the costs, particularity if a team fight goes unexpectedly badly. Did I mention you're slow?
I'm open to other (particularity cheaper) options, because at this point going to a Chrysalis can be devastating, particularly if you're ahead in levels, and it's great bang for the buck. Again, Sniper is squishy, and being too greedy here can mean you stagnate into irrelevance. That's worse, and we've sorta ignored survival up till now; the boots help, but most heroes will still outrun you, if slowly. Also, Shadow Blade is less useful if your team has other characters that depend on invisibility, Bounty Hunter for example, as the enemy team will load up on dust of appearance.
Talisman of Evasion might be a decent alternative here, though I haven't played with it much. It's a component of the Butterfly, also useful for surviveability, but it's less useful against pins i.e. Windranger.
After that's taken care of, Chrysalis is a great force multiplier and it's relatively cheap. Then lifesteal with Shadow Mask - or vice-versa, if you're taking a lot of damage, but you'll probably get both quicker if you go for Chrysalis first. Then your core items are more or less intact.
From there I promote the Shadow Blade to Silver Edge, Chrysalis to Dadelus, and Shadow Mask to Satanic. It feels like these three happen a lot faster than it took to get the Shadow Blade because by this time you're raking in gold every time you meet creeps, are a force to be reckoned with in team fights, and would benefit greatly from knowing the keyboard shortcut to send your courier to the secret shop. Money comes in that fast.
If the game isn't over around the time you buy the Satanic, you now have some pretty serous staying power. Nasty damage output, high rate of fire, and lifesteal make it so you can go one on one with just about anybody. Headshot's ministun keeps your target pinned and helpless while they get gunned down. You're still vulnerable to stuns, so some caution is required, but by that point you're carry has been brought to potential and you should be laying down the smack on the other team assuming they haven't blown the rest of your team out on the way. Divine Rapier can be a nice added bonus.
I've thought about going with Boots of Travel but haven't had the courage to give up the Power Treads, even in the late game yet, though it might be interesting to replace them with something that focuses even more on agility and attack speed bonuses while using one other slot for both teleport and movement speed bonus (Boots of Travel), though at this point that's kind of moot unless your team is behind because pretty much everything around you is going to die. Unless there's 4-5 of them and they're all level 25 and all pissed off at you.
This build focuses on rate of fire and surviveability over ult and casting, so attack speed, armor and range. Whether you go with Schrapnel DPS (I usually do if I'm ahead) or health is situational (I'm not convinced 200 health is going to make a lot of difference). I also don't know if the +4 Schapenel charges is a one-time boost or if it lifts the limit on the number that can charge up. If the latter, it's more long-term useful than if the former. An extra 100 range at this point is pretty trivial too, but it can mean the difference between getting the kill on a fleeing hero with regular attacks or using your ult (opportunity cost for later).
money spent goes toward future builds (no selling items at half cost)
early buys address specific deficiencies
high RoF can neutralize single opponent while killing them in the endgame
very powerful after lvl 18 + escape + RoF/Dmg boosts + lifesteal
uses normal attack, modified by items, to deal most damage
not extensively tested in PvP
generally run in center lane
midgame stagnation (12ish-18) can happen if your team doesn't organize a front for you to work behind
Sniper in general has to be played conservatively and focus on farming without dying
uses a powerful ult as a secondary, situational tool
I don't know if other early item buys net better dmg/rof bonuses faster
doesn't take 7.x changes into consideration or attempt to compare to builds that do (A's Scepter, what appears to be the removal or Unique Attack Modifiers which has profound consequences for Sniper)
In the early game, good teammates will help you steal kills from them, both creep & hero. Hero kills before midgame are going to be opportunistic (easier after lvl 6) but don't overextend yourself.
Midgame, you want your team out in front of you and on the sides. If you get surprised you will die, and if the enemy team is good they will focus you down early and often. If your team really likes you they'll continue to help you farm at least until lvl 12 (which is usually well after pushes and teamfights start happening). Organization is key because your teammates are likely faster than you and if you're going to make a difference in the battle you're going to do it from the rear. Also get good and feeling out a battle and when it's going badly, get out. when you're in a full on team battle and three of your guys went down and the other two are on a sliver, get outta dodge because you're already lost that fight and the best you can do for your team is not feed the enemy another kill (you). If your team is rallying around you they won't make too many early pushes beyond the first line of towers and let you farm a little longer. Also, that's a lot to expect from teammates who don't know a lot of meta, so don't get your knickers in a knot if it doesn't happen. Be patient, be conservative until you have the upper hand, and use Assassinate to finish off fleeing enemies.
Endgame, you're pretty much the big stick. Stay alert. If you significantly out-level the enemy team you can probably stay in enemy territory alone but I wouldn't make a habit of it unless you've got creeps or teammates to extend your vision and let you see what's coming. Better to preserve your outlevel than to hand one of them two because you got greedy. That said I've mowed down whole squads with this build; dealing damage is your friend, especially with lifesteal, and you can deal it out faster than they can absorb it in most cases. With Divine Rapier, you can three-shot heros at full health before they've walked a distance equivalent to their height. It's brutal.
I typically target either the enemy hero who's the highest level, the one that's situationally the most dangerous (to me or the team, i.e. bounty hunter or one with a wide AoE stun), or the one that is worth keeping at a disadvantage (i.e. enemy carries). If they run, Assasinate; if they don't, keep shooting, then on to the next. And so on. Unless your team melts first, then outta there!
Sniper presents some unique advantages and disadvantages for a late-game carry. While straightforward, he can be difficult to use early and risks stagnating in the midgame. This build takes a unique approach to those problems and comes up with a viable if nonstandard approach to herding Sniper through the early and mid game levels to create a beast of an opponent.