This is my build of Heimerdinger as I play him. You don´t have to build exactly after this build. See it more as a guide tthen a build.

I have chosen these masteries becouse i Play with them. They are realy good to use becouse you will get all the things that Heimerdinger needs. Why don´t I go for AP only. Becouse Heimerdinger is a very mana hungry champ so mana is wonderfull. YOU LOVE MANA(though mana don´t love you).

I have chosen Flash as my first summoner spell. Why? Becouse Heimerdinger is squishy, slow and ofcourse with this build focused. My second spell is exhaust. You problebly wounder why not choose clarity? You will have mana with this build and when you have bought "tear of the goddess" you won´t need more mana(if you don´t spam out rockets and bombs). And you won´t need any other escape tool becouse flash and zohna`s hourglass will do that part. TP this is not the best spell for Heimerdiger becouse if you have to leave lana then you just pop 2 turrets and let they defend for you.

With these items you will be a killingmachine. First buy meki pandant, 1 hp pot and 1 mana pot. These will keep u in lane. But the very moment you can afford the "tear of the goddess" You place 2 towers defensive at your "big turret" and recall. The enemy won´t even touch your "big turret". Then keep going as the build does. But when you have bought zohna´s hourglass you can start go a little bit offensive. Becouse the will just think your a squshi Heimerdinger and when you have placed your turrets becide you and you are about too die MUHAHAHA zohna´s hourglass and let the turret kill the enemy. For the last item you can choose between Archangel`staff or void staff depending if the enemy have bought magic resistance if not I would go for the archangel`staff.

PROS
Farming=easy peasy
Damage= no problem
Apear smal and squishy but with zohna´s hourglass you will Kill´em if they don´t consider the consequence´s before attacking.
Epic hur***
Let the enemy hunt you into a bush there you allready placed your towers=kill
Anti gank with turrets
Epic lan defender
Epic skins
CAN HEAL THE BIG TURRETS WITH HIS PASSIVE

Cons
Squishi while zohna´s is on CD
Slow:(
low hp early game
He always say he can do everything better then you

I will update this so if this heled you please give me a thumb up. If you dislike then please give me a comment of what I can do better