Full Tank Galio is also acceptable, not always Galio has to build just the AP. It's like making J4 build AD instead of tank, which that both build paths are viable. And again, try not be a mama's boy by checking out the percentage usage of items from lolking instead of finding Galio's hidden strength yourself. It's like people knowing Ryze is op AFTER Lcs plays him. It just makes you look retarded.
Another funny thing is how you refute my statement so hard in the other comments, that ironically you don't even play him.
An ideal MR item for Galio. MR for that extra AP from his passive, and the SV passive boosts his healing from his W.
Even though both are Armor items, it's still a great item for Galio whenever he uses his ult, causing the enemies to kill themselves autoattacking Galio, & melee champions taking more damage from the Sunfire passive.
For more AP passive & less interruption during ult.