this is a mid-late game build depending on your start if you have a good start you probably wont get to build the full build :)

This will help you farm and can later on in the game be turned into a deathfire grasp

It is essential to get the the of the goddess as soon as possible the archangels can wait untill after a rabadons sometimes i will get my tear of the goddess before my kages lucky pick if i can afford it.

This will provide you with some much needed health aswell as some more abilty power and some slow to help you possibly gain a kill or help a teammate to get one

OrDepending on what you need get Rabadons Deathcap or a Void Staff after your Lucky Pick and Tear. If the enemy has built alot of magic resist i go the void staff if they havnt built any or havnt got alot when you make your decision just grab a Deathcap before getting a Void Staff

If you need Magic Resist you can use to to replace the void staff

If you need Armor then use this over the needlessly and the active this item has works wonders with Heimys ult

I am not that fond on Mana regen runes because their are alot of items you can use for Mana/Mana Regen and Ability Power that i like to use the Magic Pen Runes they can help alot early and late game. However you can use Seal of Mana Regeneration if you want to they can help alot especially if you are trying to learn heimy and are having mana issues.

TELEPORT Gets you back to your lane strait away if you only leave your lane to get back your mana/buy new items your turret shouldnt lose health,it also allows you to defend any other turret almost instantly or help a teammate get a kill.

CLARITY Mostly use to help keep you in your lane early on can also help your teammates during the later game however dont use it unless you are missing some mana yourself.

FLASH This can be a better choice then teleport for the fact you can get away in certain scenarios and not give the enemy team a kill however this can be a personal preference

In a team fight stand right back and keep your turrets up because your enemy wont push to hard onto your turrets aswell as a full team however you are likely to be targeted first for this reason and because your extremely sqishy so try no to die OR if the other players on your team can fight/atleast hold off a full team heimy can push other lanes fast potentially getting ganked by the whole team or capable of splitting them up readying your team for another push on another lane.

Also if heimy goes on complete base defence it is really hard to end the game while he is alive so he can defend by himself or with 1 other while his teammates push back

In 3v3 Heimy and Shaco work really well Heimy can hold off the enemy at the base while shaco passes though the walls to get up to whatever he wants to :)

ORYou can start out with either ability i normally take the turret however if you and your team are gonna try to counter jungle getting your rockets can be viable because once you place a turret you cant place another for 25 seconds and would only be able to basic attack.

By level 5 you want to have 3 points into this so you can place your second turret.

After level 5 i put every available point into this.

If you feel like you need an extra source of damage at level 7 put a point into this, but it can be hard to aim.

If you get afirst and get alot of minion farm even without kills you can have just as much if not more gold then anybody else.
Also getting a asap so you can max it out early is important.
If you choose to use a Or Dont forget about the item actives that goes for your aswell.