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.
As I've browsed the Gragas builds, I've only seen a few Tank builds that have been very helpful (feel free to prove me wrong, I haven't searched extensively) So I thought I'd add my input on how to turn Gragas into a great tank that still packs a AP punch.
The ideal setup for me playing as Gragas involves laning solo on the top lane with one of my teammates jungling. This allows me to play defensively near the turret 2v1, and level up quickly. I choose to use body slam instead of barrel roll at early levels because the mana efficiency is much better, plus it also deals AOE damage - which is a nice way to keep farming creeps for money.
More instructions to come once I have the time to update this. Feel free to comment on what you see so far, I'm still working out the best items to buy so suggestions are always welcome