This is the most powerful AP damage heimer I've made.

When Ap is this high, your rockets do a LOT more than just harass. Turrets do 150+ per hit and rockets do 600. Your grenade also do upwards of 600 and thanks to the magic pen if you can stun with grenade in between your turrets and hit while they flee with rockets, they will go down 90% of the time

Clarity and Ghost, Ghost is good for early game and running in circles around your turret, when added to Boots of Swiftness, you can easily drain melee enemies and tanks. Clarity because heim can use a lot of mana and the rune set doesn't have much in the way of mana regen

final build, your rockets and grenade 1 hit minions and grenade can take out large groups.