hey,
this is a really short guide based on masteries/items/runes so i won't sped so much time in telling you how to play heimerdinger.

why heimerdinger?

PRO's
heimerdinger is the most fun champ to play (hehe)
nice lategame damage

CON's
quite squisy
get ganked easy by some champ ( you can proved this by plcing some turrnts in the bushes)

amplifying tome = quite nice ap for it's price and you need it to build Morello's Evil Tome
health potion = to stay in lane much longer

fiendish codex = nice CR (cooldown reduction) + ap + mana reg.!
boots of speed = to move faster for easyer escapes or getting kills.
Morello's Evil Tome = fiendish codex but much better so upgrade!
sorcerer's shoes = moving faster + magic pren(makes you a bit stroger)
angeler's staff = MUCH MORE AP LATE GAME and also quite a lot mana
rabadons deadcap = ALSO MUCH MORE AP BUYYY IT...
lich bane = ap + mana (converted into ap) and some other cool features
rai's crystal scepter = nice slows and also nice health + ap

Runes based on insame damage, masteries are basec on CR+AP(and other stuff)

i've hped you've enyoyed this guide please dont vote down because it's so short or because of my bad english.