Vayne: can kite Galio around if you dont got oracle or a ward.
Twitch: can easily outrange galio.
kog maw : outranges you easily with his abilites.
lord dominik: makes tanks very weak against adc late game.

thornmail or randuins omen is very good items to counter adc. if many in your team build it the adc gets poor in attack speed. but not every adc needs attack speed so keep in mind. these items works best vs vayne,twitch,caitlyn,sivir and special kog maw.

Abyssal makes you strong , The liandry makes you even stronger against tanks and sunfire makes you a sustain god against everyone. i prefer mercury threads because his abilties scale on MR. but you can also go Ninja Tabi if you wanna go tanky like god. Iceborn gauntlet makes you get mana whitch you will highly need. it makes you get CD and CD is very good with galio. iceborn is perfect for your passive even it makes you slow your enemy. so you can beat them up later on. spirit is just for the healing , the sustain and the CD with this build you can defeat enemy like a MLG 720 blaze it tryhard weeb lord.

You Max his Q, then you Max his E and then you Max W last. surely put points on his ult xd

ive been testing Galio on the PBE. hes so strong that full AP is bad, so instead you go this build to make him a bruiser tank top lane. this is meant to shred tanks and adc. it can 1 shot adc. remember ADC 2k17 xd

remember this champion is not meant to be played in jungle. ive seen many times players are doing it since his E and ult have gank potential. but even riot says that they are trying to make him a top/mid laner.

You got 3 choices between Deathfire touch , colossus or grasp. i prefer grasp because of the passive galio got.