Is it better to build gragas support ap or tank?

I would say take Spellthief's Edge early into ap tank items. The item is so gold efficient, if you can poke.

Tank, if you are taking gragas support, you are taking him for his CC right? So build tanky so you can get off your skills and soak damage and potentially get off more abilities. You aren't trying to get out a bunch of damage, but setup plays for your team to get the kills

I use Gragas support only as a tank. If you go tanky your q will do zero damage. The only thing it is good for is slowing your enemies if you are chasing or kiting away. Start with Targons, 3 cookies and a mana pot. Max e, then w, then q. Don't bother using your Q to poke since its damage sucks and wastes a lot of mana. Take advantage of his passive. What I mean by this is between levels 2-4 you can usually win any trades if you successfully land your e/w combo. Drink your W in bush, E at the support or adc, smack them with your barrel. Trust me when I say that it does a bit of dmg early game. After doing that you can just walk away, drink your flask and pop your passive with a potion. Instantly go from 60% HP to 90%. and repeat this since the enemy adc only has 1 potion. If you're ahead in lane get , if not just get CDR boots. If mana is a problem you can go frozen heart but I suggest a randuins or aegis pickup depending on their team comp. Try to get as much cdr in with your tankiness. Land a pick with your E/R or peel for your team. But trust me when I say support tank gragas is underrated. Hope this helps. Look up my IGN: Column34 if you want to see how I build it. Cheers.