I use this as my top lane heimerdinger build. it is simple but effective. you really rely on your itemes, so make sure you get most of the minions in the start with your turrets. once you have the levels and money, but the needlessly large rod and start farming minions (and if possible some enemies) at the lane you're in. Once you have enough money, buy rabbadon's deathcap. once you got that, just go on buying rods and upgrading them to scepters. this ensures your health is high enough to survive a lot while still dealing giant amounts of damage with your turrets. Your turrets are the best way of outputting damage and sometimes when they are low use your rockets on the enemies to kill them. if you want to deal a lot of damage just use upgraded rockets. if there is a single enmy you want dead, just stun him with your grenade and build turrets around him.