From playing him a bit RoA seems like a strong purchase that helps out his naturally slow scaling with a fairly safe laning phase and an even stronger mid game spike. Abyssal can be decent into AP Matchups and gives some nice stats since he still scales pretty well with magic pen and Abyssal provides the same functionality as magic pen but vs teams with a lot of AD Spirit seems stronger since you need quite a bit of armour and health to get past Lethality.
IBG has been successful from what I have seen and provides a strong spike. I have yet to see a sunfire cape and I believe this is because Galio already has decent waveclear so he doesn't get much for that and he tends to sit at range until he goes in so it doesn't provide much laning power compared to other tank top laners who will constantly get traded on when they try to CS. Of course that may have to do with people being wary and keeping their distance from Galio since no one really knows his damage output and the people playing him are always eager to fight. This means we could see an emergence of sunfire cape after a couple patches.
Boots all tend to be mercs/tabi from what I have seen. Haven't gotten to late game too many times but GA seems to be the consensus. With Crit still barely existing Randuins aren't making much of an appearance although I imagine the item is still good since he can use it before he activates W. I saw one Void Staff on a very ahead Galio and he was definitely putting out the damage, but eventually he did fall behind in the tank department.
As a side note for those interested he seems very capable of jungling, even able to clear chickens without much issues at level 3. He is a bit mana/CDR dependent early but doesn't have too many issues as mid rolls around. I personally went for runic echoes over cinderhulk since I wasn't sure how hard mana costs would hit. I am pretty sure that with just a hunters potions you are pretty sustainable though so I would probably go cinderhulk next time as I felt very squishy for a lot of the game. He has a pretty decent clear, nothing Vi or Lee speed but definitely a step up from most tank junglers.
with 
for the early game burn damage. even then I would probably sell it later.
His AP ratios just don't seem worth building AP for, just like Sion's AP ratios aren't really worth building for. You start with 1 or 2 
and that's all the mana regen and damage boost you need early game as E max sion. I feel like this will be the same for Galio.
, but I feel as though 
and even then i probably wont build more then 2 ever
