Gragas is a wonderfull AP carry. Hes barrel roll will get the job done. Gragas as a good survivalbility and Ranged attack to keep you alive.

Gragas is a very powerfull Ability power champion. Hes main sort of damage comes out of hes barrel roll so its important to max that one out first. As every other champion you wish to continue harressing your opponent in the lane with your barrels thats why its usefull to have an efficient mana flow, thats why we take that extra drink to gain mana as a second skill. I use mainly the E as an escape or attack skill thats why i keep it at level 1.

Pros
+ Very powerfull
+ Good mana flow
+ Average survivalbility

Cons
- Bit long cooldown
- Requires practice to aim
- A skilled player can avoid your barrels

Gragas is a perfect farmer on minions. Hes barrel roll can become a one-hit kill wonder on level 7 already. The more minions you kill the more items you gain to strike fear in your opponent. This is also a very good push way.

Greater Mark of Insight Red mark
As we trow our barrels we do not want our enemy to absorb a low amount of damage. What we do want is to penetrate there defendses and do as much damage to them as possible

Greater Seal of Replenishment Yellow seals
Mana regen is very important in level 1-5. In those levels you go out of mana very quickly.
Why flat mana regen instead of per level
Yes indeed the per level seals will become better then the flat when you hit level 6. But whats important here is that you only need to have a mana regen in level 1-5 wich drain the most mana. at level 6 you have enough mana to process further with your flat and W.

Greater Glyph of Potency Blue glyphs
Greater Quintessence of Potency Purple Quintessence
Ability power is the main focus in this build. the more you gather the more damage you inflict.

Items are your main source of upgrading your damage. however they are depended on your enemy. Here you see a preview of a item sequence i used and worked well for me. however if you have mana issues i prefer you to take Archangel staff before Deathcap. There are many other ways to make this item build different but your main focus should stay at Ability Power upgrading.

For AP Gragas i use a 9/0/21 build with improved mana regen and experience. I do want to take the buff duraction upgrade for Baron and Blue buff for they can help you increase survivalbility and mana regen.

For summoner spells i take Clarity and Flash

Clarity
When your in the low levels your mana will eventually run dry. altough we have flat mana regen we can keep casting every time our CD hits 0. Clarity will give us the extra boost to continue our harressment. Do keep in mind that you can use it to assist your lane partner.

Flash
Imagen a lane full off minions.. Your E wont help you there. altough you can move trough small walls, your flash will help you get further. Use your E on a small wall and as you passed you find out that there is another enemy on that side. well Flash is your solution to surpass that champion and flash over another wall to safety.