You can have 5 picks and your boots with in 15 min in, they give a 125 AP boost which is deadly early on + the gold boost and by 30 min I have this build complete. With this my grenade hits 900+ rockets 950+ and turrets 350+ each.

http://www.mobafire.com/league-of-legends/build/heimer****-3246 check it out

http://www.mobafire.com/league-of-legends/build/heimer****-3246 check it out

http://www.mobafire.com/league-of-legends/build/heimer****-3246 check it out

ohh with build and 9 greatermarks of force 9x greater seals of force, and 9 greater quints of force,
turrets hit 291dps each ( attack speed of 1.25)
934 for each rocket
bomb hits 829, ive hit people up to 1k though this is just figures ive worked out

ever thought about trying out a archangels staff, works wonders early game with mana boost, also with that much ap lich bane is kinda useless i find that people die way before i can use a physical attack, and if your mid you shouldnt need kage's lucky pick you will get alot of money by killing creeps, i find that buy 45min i can end up with 2xarchangels staff, 1x zhonyas ring, 2x void staff, and sorcerers boots, i hit for around 800 with conc bomb, rougly 700 missile and my turrets hit for 200 each shot(without runes aswell), people die really quickly especially if they are stupid enough to flash in to att me, ive killed 4people in a row due to turrets(by myself aswell) i finish alot of games around 15-3-(10-20 depending on how good team is