dont understand cowardly a coward would hide behind he's second turret and just let he's 3 turrets also those he can use and just get exp from that and would only go to hit the enmey turret once in a while with the grenades, and have fortify ready at alltimes. heimershouldent go so ofensive build he,s more of an "no you can't take this tower" guy while going support for his team. and it cant' be the best build if you think of the -2 rating yuo have of some reason.
btw. i would drop chalice and rush catalyst instead and get rod of ages after mejais.

ok imo best heimer build

Rod of ages
Mercury boots
mejais
erm the mana->ap thing
zhonyas
rylais

Why would you get RoA so late?
It's a complete waste and you're never going to get it anyway.