This build is based on the "Heimerdinger - QQ Rockets" build by: JunSupport so big thx to him.
There's only few modifications that I made into his build making it even more better than it already is. This build takes advantage of heimerdinger's passive and pushing abilites.
Modifications in detail
As mentioned, this build takes a huge advantage out of heimer's passive making him almost immune to harrasses at early game having at least 23 hp/5sec regen with sapphire crystal. With promote and 2 turrets you are able to basicly destroy every unguarded tower by yourself.
With this build you give up some of heimerdinger's abilities to own someone in 1v1 you are much better at doing what heimer is best at: winning.
What I like about this build the most is its ability to adapt to the situation. What I mean is that if you notice that enemy team doesn't have a very strong AP side you can ditch the abyssal scepter and take rabadon's deathcap to make you (and your turrets) even deadlier! Or you can do just the opposite and build e.g. Thorn Mail to keep you in battle longer After the Tear of goddess you basicly can determine your build order. But this order is the order what I usually pick.
I really didn't enjoy the Will of the Ancients in JunSupport's build since the turrets aren't giving you any health and didn't quite realize why didn't he add the Rod of Ages in the build since I think it is the most important item for heimerdinger. Rod of Ages + Archangel Staff gives you a health regen bonus (with the masteries selected of course) so huge that you're making Dr.Mundo jealous.
How To Play
I'm dividing this into three different parts, which are: Early game, Pushing(midgame), and teamfights(endgame)
I'm going to tell you as if you were playing at the mid lane but of course you can lane at sides also.
Surprisingly you are playing very defensively. Try to keep the minions fighting at the middle of the map. When you notice enemy jungler is dead/ganking other lane, you strike. Use the promote and kill as many minions as you can without turrets and also try to harass enemy laner while doing that. You put your both turrets attacking at enemy turret and leave (unless you know where enemy jungler is). If the enemies don't have a jungler... well it's bye bye mid lane then. Soloing blue at lvl 5 is easy job with 2 turrets so with this you can easily harass enemy champion.
Never go in for a kill alone! Killing the enemy laner is a great help for you but it isn't mandatory so if you really want to kill him/her wait for your jungler or other assistance.
After you've got the enemy turret you and your possible jungler are going for top lane. You strike in very fast so the enemy mid laner won't be able to come help solo laner soon enough. You (and jungler) try to gank the enemy solo laner but it's not pity if you don't get him. After the gank you land the promote and push your way to turrets without your turrets. Again land your turrets at the enemy turret and all 3 of you should get the enemy turret.
Now farm and repeat this at the other turret and you have 3 of your opponent's turrets down.
Remember! You can't always go by the book and sometimes you have to improvise. If it seems impossible you don't have to push exactly that turret right now.
If the map is well warded you can continue doing the same as mentioned above: Promote, hard push, dump evolution turrets and leave.
But in most cases the map is poorly warded so you can't do that. You CAN go use promote on different lane and come right back where you came from. But now on it is really dangerous to go all the way to the turret since your enemies are expecting you to do so.
But let's go to the business: the teamfights.
Heimerdinger is of the best mages during the teamfights and he is often focused because of that making rod of ages and zhonyas hourglass a "must have"-package. If there are no minions near by, put the durrets on ground, pop ulti and start flinging grenades and rockets everywhere. Put the turrets pretty close to eachother but not too close. A Range of 200-300 apart from each other is fine. This serves as "battle bunker" at the fight. When you are getting attacked you run into this "battle bunker" and stun him with grenade, spam rockets and possibly use flash and let the turrets do the rest. If enemy ad carry is trying to kill you, you most propably end up getting a) a lot of free time for your team or b) an easy kill.
If there actually are a lot of minions nearby I suggest to do just the same but after the turrets has been deployed, especially if you are targeted stay far behind so you don't get killed. You can and you must go in to throw grenades but the minirockets aren't now a sure hit since the minions nearby. If you stay far away it should take a long time and effort for the enemies to reach you while you are still in the teamfight with almost full potential.
Everything can't be described with words and that's why I suggest you to look out for some heimerdinger gameplay videos (e.g. Heimerdinger Champion spotlight) to know properly how to gank and in what situations and so fort.
Don't wonder too much alone with heimerdinger since he is really one of the best champions when it comes to teamfights.
He isn't the best champion on 1v1 but the games are won by the team who gets most turrets and wins most teamfights.
Thank you for reading, sorry for possible poor english, typos etc. :)
And why did I make this guide? Because "I could help you do that better"... So I did!