Heimendinger is a really good AP champion however he is a really squishy so you have to be careful with him, in this build I will be showing you my options on what I would use for him, you do not have to do it my way but I would like to show you and you may or may not choose to follow these. This is my first build guide so please tell me any ways that I can make it better for you.

Heimendinger's Pros:
[*] If built correctly he is a force to be reckoned with he can do immense damage in seconds.
[*] His turrets can easily destroy a wave of minions and destroy towers with ease and if placed correctly can be really defensive.
[*] He can be used for jungling however i have never tried this but i have heard that he is very good.

Heimendinger's Cons:
[*] He is a very squishy champion and therefore he can feed if not careful, but if fed he can very OP.
[*] If you do not have any masteries then he will be under powered and will do no damage/little damage.
[*] He is not very good when teamed up against and therefore needs to not push too far ahead in games, it is advisable to stick with team mates later game.

I chose these items because they will help him do AP damage and have extra mana/regen/speed/cooldown. The best thing to get is doran's ring as this will make you OP in early game, then next thing is boots now you can get sorcerers boots without the upgrade or with it, i would advise getting this because it will give you more speed so you can enter and exit the battle a bit quicker. The next thing to get is the archangels staff now this is very useful even without the upgrade, but with the upgrade it is x2 better as it adds 1000 mana and then you can continue fighting without the worry of low mana and also you have more AP. The Rabadons deathcap is mainly for the ability power as it does and extra 120 AP not only that but it increase your ability power by 25%. The Liandry's torment is to give you more ability power and health. I got Shurelya's reverie because it gives you more health and more regen so you are not as squishy also all nearby friendly champions gain a 40% movement speed. Finally i would sell dorans ring for Deathfire grasp, this is useful for two things, one for the ability power and two it as cooldown reduction so that you can sue more spells that do a lot of damage.

The best way is to only start buying runes at level 20+ as that's when you get the good ones, it is also advisable for you to save IP as it can be costly depending on what you get.
For my Quintessence i chose:
[*] Scaling Ability Power.
[*] Scaling Mana.
[*] Scaling Mana Regeneration.
For my Glyphs I chose:
[*] Scaling Ability power x3.
[*] Scaling Mana Regeneration x3.
[*] Scaling Mana x3.
For my marks I chose:
[*] Scaling Ability power x3.
[*] Scaling Mana Regeneration x3.
[*] Scaling Mana x3.
For my Seals I chose:
[*] Scaling Ability power x3.
[*] Scaling Mana Regeneration x3.
[*] Scaling Mana x3.

For my masteries I chose 25 in offence and 5 in utility, the 5 in utility is only to give Heimendinger a little boost on speed and mana, the 25 in offence is all to do with magic damage/AP.
It is all magic damage because he is an AP champion and AD will not do much help for him.

Heimendinger is very useful when it comes to team work as in battles he can place his turrets down when the enemy is low health and then it can kill them easily, his grenades can stun enemies giving your team an advantage, his rockets are really good at damage dealing and his ultimate can make his turrets twice as powerful and also has a slow ability. However even though this is good his rockets can hit minions so it is advisable to kill them first also his turrets will attack minions so he needs to be ready to place them down at the correct time or else they will get destroyed by the minions.

Heimendinger's turrets are the best thing to get rid of a minion wave and also when they kill them you get the gold so then you can buy more items with this and become more OP.

I tend to get my rockets first as they are the most damage dealer for early game, I do not get the concussion grenade till later as it does not do much damage early game and therefore I upgrade my turrets and rockets, I get my ultimate at level 6,14 and 16 because I do not think it is the best ultimate and it only upgrades your turrets for slow, however it is useful for healing the turrets when they are damaged.

Thank you for looking at my build guide for Heimendinger, I would just like to say again that this is the options I chose you do not have to follow this but you can if you wish, if you have any ideas how i can make my future builds better please comment. Also I am called Zinq Murphy so please if you want to add me please do so, I hope to see you on the battle ground some day.