Most people assume you have to build galio around magic resist . really i feel he's much better picked first so people try to AVOID ap champs.

rush tear of the goddess as quick as possible. once bought use your W as your running back to lane aswell as your E. try to build that baby up

get a giants belt. the extra health will go a long way with galio and should be your first buy after the mana tear, after get a mercury treads. we are getting it mostly for the passive but the mr is a nice bonus

seriphs embrace is a much better pick than the typical athenes unholy grail. pop that item right before ulting and youll let the item take most the damage. on the plus side it gives way more ap aswell and you never need to worry about mana. the zhonyas will hurt your dmg with your ult because you won't receive dmg. if you keep zhonyas for an escape it works better

Q has massive range so use it to zone out enemy champs , try to aa minions early game to keep mana up but later on you can E Q combo to clear most of any wave. try to get your opponent to about half health and then charge with E Q R Q . that combo kills most champs pretty easily .