This build is mostly suited for solo mid or solo offlane, but it can work with dual lane too. It is NOT suited for trilane at all. You will be focused mostly on powerful disables, and later on, high damage output. This build may be played as a support, but it will lower your late-game potential, and will leave you in a support position for the whole game. With the right set-up, Invoker is a nuker whose power doesn't drop off later on.
-Decent damage output at all stages of game
-Great for ganks and teamfights
-Not as squishy as most mid laners
-Great escape mechanisms
-Vulnerable to silences
-Vulnerable to invis heroes
-Low survivability in teamfights
-Hard to farm early game
Starting with blades of attack provides you with a good boost to your last hitting and harrassing power, while tango makes sure you don't have to go back to base (While others would pop salve, you toggle Quas on, eat a tree, a stay back a while, and you are okay.), and the branch provides a little bit of attributes, and later builds into a magic wand. While you want to get your scepter as soon as possible, be sure to take drums and boots first (Magic wand help a lot too). Phase boots give your so far slow hero a nice speed boost, and the damage bonus is great for invoker. Drums give you stats and allow you to have haste (with your phase) later on (helps a lot, allowing you to outrun nightstalker at night in some cases). Sometimes you want to take Eul's before scepter, when you are fighting some hero with a strong spell that you can dodge (for example, Huskar's ultimate). When you have your core, be sure to get a MKB (will explain later on). Mjollnir gives you a HUGE pushing potential, and great attack speed to allow you to have your E toggled on. Eye of skadi ensures nobody escapes invoker's wrath. BKB or Heart might be viable choices when opposing team starts focusing you down in teamfights, or when enemy has heroes with high nuking potential (Lina hurts), Invoker is still an intelligence hero, and despite his bonus strenght from Q, his health is still low. Bloodstone helps since invoker's combos cost a LOT of mana. Blink dagger and force staff help when the enemy has good escape heroes (For example Nightstalker or WR) and help a lot to drop ice wall in teamfights. Orchid gives great mana regeneration, and a good silence, which can, for example stop silencer from dropping his silence, which could otherwise get you killed. Shadowblade might be a viable choice if you find yourself in trouble often (6.78 dropped the Ghost walk cooldown greatly, so it probably won't be neccessary at all).
Early on, you will focus to get as much last hits as possible (Boots finished before 5 min mark) and you have great position to harrass with your cold snap, and your Q makes it nearly impossible to harrass you out of the lane, even with a necrolyte or Kotl against you (however, lion can prevent you from harrassing, as you need the cold snap bonus damage due to your low damage). You can definitely gank after level 7, with your tornado and cold snap up, provided your teammates have some disables, none shall escape death. ALWAYS keep at least 240 mana, in case you needed to ghost walk away quickly. Even early game, it's really hard to kill invoker, even if they have vision (ghost walk slow is really nice).
Once teamfight begin, you want to drop as much non-exort based spells as possible (except for alacrity and ice wall). Your typical combo should be Tornado->EMP->Deafening blast, Cold snap the carry, toggle W and Ice wall the fleeing ones. EMP puts the opposing team in a bad position, since everyone but intelligence heroes will be out of mana (no ult for CK or SK). At this point, you are quite vulnerable, since your only serious damage are full combos, and your right-click is still really weak. Again, you will want to keep mana aside for ghost walk. 3rd level of Invoke isn't always at lvl 12, since you need at least half of your scepter farmed up (If you have it at lvl 16, it's not the end of the world). 60 mana cost invoke kind of hurts, so you need to get scepter quickly. Usually you don't want to have Invoke lvl 2 when you get scepter, since you would have to wait a lot for another level (Some exceptions exist, if you have scepter before lvl 12, it's only good).
The fun ends (starts!) here. Once you have your monkey king bar, you start dealing massivve damage, putting you (kind of) in a position of hard carry. Toggle E on, alacrity yourself, and watch the enemy melt. You can certainly drop your spells for some CC to keep them away from you, or to prevent them running. With Mjollnir, it's even better. once you cold snap someone, they are stunned constantly even if you are alone. In teamfights, you want to drop as many spells as possible (for example - Tornado->EMP->Meteor->Deafening Blast->Forge spirit->Alacrity yourself - That surely needs a lot of practice). Also, you can now sunstrike running enemies, which takes a lot of practice to always hit, but with practice comes strenght and you will often be able to kill them with a blind sunstrike. Eventhough Invoker is fun overally, I like this part the most. Again, ALWAYS keep mana for your ghost walk.
Invoker is a nuker whose power never vanishes. Eventhough he later becomes a furious right-clicker instead of a nuker, but he hurts at all stages of the game. Early and mid game, you should be cautious, since you are made of paper, and heroes like nyx completely destroy you. Anti-mage is a bad counter to invoker, but with early ganks, he won't ever be a problem. This build takes a lot of practice, the knowledge of the spell combinations and the ability to invoke them immediately are essential to high-level play, but even without that, invoker isn't hard to own with. Please give me feedback, so I know what to avoid or add in my next guides, or how to fix this one. Good luck, and have fun!