Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
this build focuses on Galio's impressive spell power and decent health and very nice magic resistance. early game, your amplifying tome will give you a little kick to your spells, allowing you to harass early on. after a while, turn that amp. tome into Sheen for some decent attack capabilities with your spells. Turn sheen into Lich bane and get a very nice amount of ability power. this will add some spell res. and give you stronger spells, movement speed and a little mana. Afterwards, get Sorcerers boots and Abyssal Scepter. This will give your ultimate a strong edge to all enemies affected, and give you some decent spell penetration. After that, buy another negatron cloak and build Banshees. This adds some survivability and prevents an unwanted silence or stun during your ultimate. zonyas and Will of the ancients give you lots more spell power and some spell vamp, allowing your spells to heal a fairly large amount. for this build, i recommend flash (for positioning your ultimate) and fortify as a safety,and a powerful punch to anyone who gets tauntet within tower range. The runes give you some more magic resistance, ability power and movement speed. MS is pretty important for galio, because his only two offensive spells are medium range, and medium cooldown. Depending on the game, you can switch Will of the Ancients out for Rylais Scepter, which gives a very generous slow, and gives a fantastic advantadge when using Righteous gust.