Well, this is one of my first guides. It was really hard making this build because of the squishiness Heimerdinger has. He is extremely squishy at the start and requires lots of skill to not die. I play Heimer as a middle laner. He is an extremely good harasser and can farm very well. His turrets and his grenade make him unstoppable. His turrets prevent ganks because of his ultimate. His ultimate makes the turrets shoot freezing bullets which slow the target. Make sure you do not expose yourself too much or you will not be happy. He is an extremely good pusher with lots of power behind his spells Again, this is one of my first guides so please no offensive language or spam. Thank You.

For the masteries I take 9-0-21. You may also get switch offensive to defensive if you find him too squishy.

For the items, I get Chalice of Harmony, Sorcerers shoes, Rabadon's Deathcap, Rylai's Crystal Sceptre, Rod of Ages, and Zhonyas Hourglass. The reason of ZH (Zhonyas Hourglass) is in team fights. You run in with your turrets as I said in the introduction. If you get targeted, which you always do, you activate and let your team and your turrets weaken the enemy. Run when you become vulnerable again. You may also switch Chalice of Harmony for a more mana increasing item.

For the skills, you HAVE to max our your turrets first. His turrets are what make him a useful champion. You can either grab rockets and/or grenades depending on what you like more. But you have to max out his turrets first.

For the summoner spells, I took Ignite and Clarity. These two spells are well while in middle lane. Ignite is for those pesky flashes that you can't catch. Clarity is used for his mana (obviously). His mana is drained so fast after you upgrade his grenades/rockets you can't use mana potions to cure it. You need clarity for sticky situations where you need your ultimate. You can also take Exhaust instead of Ignite.

PROS
[*] He is extremely well early game
[*] He prevents ganks like a beast
[*] He is an ability spammer
CONS
[*] He is extremely squishy
[*] His mana pool is low
[*] He is usually the main target for team fights

Heimerdinger is one of the best farmers out there. His turrets are awesome once you hit level 9. With enough ability power, you will be one-hitting minions with all abilities. Farm whenever you can.

Heimerdinger is a very unique champion. His turrets are his main source of damage. Without his turrets, he's just a crazy inventor with rockets and grenades. His ultimate boosts all of his abilities. He is a fairly easy champion to use.

This is what you do in team fights. You set up two turrets and stun with the grenade while they are in range. Shoot your rockets and your grenade as you activate your ultimate. This will be devastating to the enemies health. Run back and wait for your skills to be usable again. Repeat until your team or the enemies is dead. You may also catch the stragglers with a grenade over the trees or a rocket to the face. Just make sure you do not get cocky. Heimerdinger is very squishy.

This is the summary: Heimerdinger is a squishy mid laner champion. He can push fairly easy and is well early game. His turrets are his main power source. His mana pool is small so be careful. He can prevent ganks like a boss. He is a fairly easy champion to play as. He is one of the best champions out there in the League. (My opinion) XD
Hope you enjoyed. You can also check out my Malphite and Corki guides. Those aren't that great but they cover the basics. Please like and leave a comment. Thanks again.