Why two boots? I get early mana boots because it allows me to always have devour mana and let me keep my aggression up in lane when my enemy lane hero hits my level death. Doom is very slow and this lack of mobility really hits him hard, so I pick up phase boots after to give me that edge on move speed and some nice base damage. I disassemble my mana boots later upon completion of my Blood Stone. So I basically pay 250 gold for a team mana battery early on, which is only 2 devours :)
Bloodstone- This item is amazing, especially if you can get it quicker than most heroes via Devour gold. This will also keep you from running out of mana early to mid game since you will be using the Chain Lightning neutrals or even the shockwaves depending on what you choose, not to mention the reduced death timer/ gold lost and AoE heal on death.
Blink Dagger- This item will allow you to blink in and initiate on high priority targets and open them up with Doom, or even a Centaur Khan devour stun or Satyr Trickster Purge. It adds a ton of mobility and survivability.
Disco Veil+ Blademail - These two items work amazingly on Doom. They will make up for his lack of armor and combos amazingly with your Ultimate ability "DOOM". The Veil of discord debuff last 20 seconds which is a hell of a long time especially when the enemy has a 15 second DoT on them. They will wish they were dead and they will be. On top of it being fantastic with his skill set your team also benefits from it as well.
Blademail will give you extra damage output with it's active and 22+damage while your Level Death is on cooldown and countless other scenarios. Together with the combined health regeneration of Bloodstone (9hps) and Veil (5hps) on top of Scorched Earth's 30hps you'll find blademail offers a lot of damage return opportunities.
Alternate armor slot (instead of blademail+veil)
Shivas - Will grant an excellent anti-carry attack speed aura to shut down manta and illusion heavy carries, and will also supply you with a gap closer via it's activation.
Aghanims- **** load of health and stats, makes his ultimate even deadlier.
Refresher - Two is always better than one.
If you plan to jungle I can't really tell you which neutral ability to take since the spawns will be random for ever game, but I can say that if you can get a net neutral with the skeletal summons that is your best bet for successful jungling. Alternatively you can get a Thunderclap neutral ( Furbolg camp ) and stack the small camps a few times and clear with thunderclap. If you get a Wildkin you can stack a hard camp 3-4 times and just about clear them with a full duration tornado. This guide wont be much about jungling so I'll leave that to another guide.
This particular Doom build will be an offensive caster doom build. Relying on heavy mana to dish out damage and smart neutral abilities to maintain the upper hand in battles.
First 1-14 minutes - I almost always will want a Satyr Hellcall as my devour neutral. It will give you a 125 damage nuke with a very low cooldown, but more importantly a 4 health per second regen aura. This will keep you in lane during the rough part of laning phase and will allow you to skip early ring of health which is commonly seen by Doom players.
14 minutes to 25 minutes- As a caster Doom you will want this guy which offers Chain lightning. A mana intensive spell, but considering you will be first buying a Blood stone it shouldn't be too big of a problem.
25 til the end of game - At this point you should have your blink dagger. This will give you the option of two neutrals.
Centaur Khan- Having this 2 second stun and a Blink Dagger will allow you to blink and initiate just like Centaur Warchief would! Considering Doom is so innately tanky health wise the opponent will most likely not target you after you initiate which is a huge perk. The attack speed aura is just an added perk for your team.
Satyr Trickster- This little guy offers one of the strongest abilities in the game both offensively and defensively. A 5 second cooldown purge that completely stops an enemy in it's tracks, and removes all of his buffs. Or use it on your allies or yourself to purge off all debuffs. I can't count the amount of times I've countered a Bounty Hunter just by constantly removing the Track debuff from my allies. It's great for removing Blood lust, Ursa's Frenzy and Enrage and too many others to list, you get the picture. This also combos very nicely with blink dagger since in order to Purge an enemy you have to be near melee range, same with cleansing allies.
Remember! It's only a 5 second cool down! So Abuse the hell out of it! Literally insane on caster Doom.
Now note you don't have to keep these neutrals but these are the ones I recommend using as this heavy mana reliant build.
Hope you all have success trying this build out. Here is a video for some insight on how to play the build out.