This is a short and effective guide to master the ways the big fat Gragas as an AP caster, mid or top.

Abbreviated Terms
CC = Crowd Control (Stun, fear, slow, snare, etc)
AP = Ability Power
AD = Attack Damage
MPen = Magic Penetration
CDR = Cooldown Reduction
HP = Health/Health Points/Hit Points
AoE = Area of Effect
MRes = Magic Resistance
MReg = ManaRegen
HPReg = Hit Points Regeneration

Pros

Good AoE slow with bodyslam
Massive burst from good ap ratios
Great lane sustenance with Happy Hour and Drunken Rage
Free flash every few seconds with Body Slam
Can interrupt enemy teamposision, deal massive AoE dmg with Explosive Cask
Low cooldowns
Great farmer and hard too tackle in lane due too his great dmg and lane sustenance

Cons

melee autoattacks

Gragas needs his masteries to help bring out his massive burst, and also keeping him healty.

With 9/21/0 you get a good MPen, ap and cdr, as well as buffing ur survivability to great levels.
This really gives you a great advantage early on in lanes vs bruisers and dmg-dealers, wich you are sure too meet if you play top solo or mid.

the reason why you need so much on defencive is too constantly be able too harrass with both
Body Slam and Barrel Roll without being afraid of taking a hit or two. with you passive and these defencive masteries you will be a "pain the the lane", dealing tons of damage and constantly healing up passivly with Happy Hour.

These masteries are also good mid-lategame to keep you not too squishy, since you can get quite wounderable midgame with this build.

A good Gragas is somewhat impossible too take down 1v1 in lane.

When it comes to runes I like to build them like this:
Greater Seal of Scaling Mana Regeneration x9
Greater Glyph of Scaling Ability Power x9
Greater Quintessence of Ability Power x3
Greater Mark of Magic Penetration x9

There are ofcouse many good varities of runes that fit Gragas great, but the reason i have chosen these runes is; It gives great burst early on in game, gives a solid manaregen together with Drunken Rage for lasting in lane early on.
I choose the Greater Seal of Scaling Mana Regeneration and Greater Glyph of Scaling Ability Power that scale over time, since you get a solid start-ap from the Greater Quintessence of Ability Power, and Dorans Ring. It really pays of later in the game where you ap pr.level scales up to get tree times better then the flat ones (at lvl 7 they are allready as good as the flat).

I like to be able too spam kegs mid and lategame without depending on the bluebuff.
But ofcourse, you should snatch the bluebuff as often as possible.

As for summonerspells i allways go for:


Flash is a great spell for Gragas. it makes you extremely hard too catch together with Body Slam. Its really like having two flashes if you use Body Slam correctly.
Flash can also be used to initiate together with Explosive Cask and Body Slam to catch that guy who sticks around for a bit too long after his team left or just for fun surpriceattacks.

I rarely use Flash for initiation or chasing, since you really need it in bigger fights where you will get targeted. It will increase you chanses for surviving getting targeted greatly. It is important for your team that you get to use ur abilities effectively.

Ignite is a powerfull spell for finishing of those who try to escape Gragas, or for keeping those high selfhealing champs easier too bring down. its also good for using on those champs you know the supporters will try too heal.
Ignite also gives you a great shot at getting kills in lane early game.

jumpig two walls and escaping with 10 hp Gragas? No problem!

I tend too go something like this. It happends that i change the order slightly depending on who I lane against, and how fed I get.
I always get Barrel Roll first, Body Slam second and Drunken Rage third.
the reason is simple. at level 2 you already deal alot of dmg with Barrel Roll and Body Slam and you have the chance to get early control in your lane, and often FB by constantly harrassing with good damage on Barrel Roll and using Body Slam acationly for initiation or possibly for escaping if you do somthing dumb or get early ganked.
Too keep your mana healty you shouldnt spam bodyslam too much early on, and you shouldnt need to.
At level three with Drunken Rage you should be a real pain, taking reduced damage, dealing extra melee-dmg and regening mana.
I tend too get most of my FBs on level 2-3. You should attack like this: use Drunken Rage, Initiate with Body Slam, autoattack, Barrel Roll, auto attack. if you get the chance you follow up with Body Slam, Barrel Roll.
Ofcouse the timing of you initiation is important.

after level 3 you should max Barrel Roll for max dmg output, taking Explosive Cask on level 6.

when you have maxed Barrel Roll, I often level one more Drunken Rage for more usefull MReg, dmg-reduction.

now you max out Body Slam taking Explosive Cask when possible. and at the end finish the Drunken Rage

Start with Doran's Ring. This is a great startitem for Gragas, giving you some ap, good MReg and a usefull amount of health. this helps you alot with keeping you mana healty, boosting you burst and allows you too be more agressive early on.

At the first shopping trip home you should it depends alot on how you are doing what you buy, but you allways get Boots and a sight ward on first trip home.
If you get a desent farm and are earning good money you should aim for early Sorcerer's Shoes and Rabadon's Deathcap.

I start out with Doran's Ring, on first trip home i get Boots and a Blasting Wand. Sorcerer's Shoes if i can afford. If i get really fed i get Needlessly Large Rod instead or blasting wand. i prioritize getting Blasting Wand or Needlessly Large Rod before finishing Sorcerer's Shoes.

If you really struggle in lane and are home for a early trip you can get a early Ruby Crystal, later finished too Catalyst the protector and Banshee's Veil.
if you are really in the gutter, you can finish the Ruby Crystal into a Heart of Gold.

after you have finished Rabadon's Deathcap and Sorcerer's Shoes, you build after whos on the enemy team. If they stack MR, and you dont feel too threatened by them taking you out, you should go for Void Staff next.
if the enemy team are more agressive and deal alot of dmg, making you feel a bit woulnerable, you should get Catalyst the protector before your Void Staff.
If they deal heavy ad you can get your Chain Vest after Catalyst the protector.
in rare cases if you meet a team without high ap output or decent cc you can drop the Banshee's Veil. In that case you should get Sunfire Aegis instead of Banshee's Veil.

Now you should have Sorcerer's Shoes, Rabadon's Deathcap and Void Staff and Banshee's Veil. now you get after what you need. if they deal heavy AD you can go Zhonya's Hourglass and Frozen Heart,
On heavy AP teams you can go Abyssal Mask and Lich Bane.
If they deal both decent AP and AD, get Zhonya's Hourglass and Lich Bane

you can also consider swapping your Sorcerer's Shoes with Mercury's Treads after getting your Void Staff.

As i mantioned earlier you should try to harrass your opponent as much as possible. I prefer getting top lane with Gragas, since it makes me less woulnerable for ganks and you can be more aggressive in lane.
You should be able to harrass without pushing the creeps too much. Sometimes its impossible too avoid creeps pushing a bit. If your opponent mingles alot with the creeps, making it hard for you to hit him without pushing, you should after getting Drunken Rage, go into creeps and auto attack him with the extra AD you get. if he runs out of the wave, follow up with Body Slam and Barrel Roll.
If he starts chasing you, you do the opposite; Body Slam for slowing him, and Barrel Roll.

After your first trip home, where you picked up a sight ward, you can play more agressivly, killing of creeps and harrassing with Barrel Roll. you can keep pushing hard in lane and being a constant threath using Body Slam if the opponent comes close enough, slowing him and giving you the chanse of dealing dmg with Barrel Roll and auto-attacks.

you should be safe in the bushes if you are pushing in lane, being aware of gank and using your Body Slam to escape, or in worst case Flash if you get caught.

On level 6 you have a massive burst. You should attack like this 1v1: if he is trying to stay away from you, but you get an opportunity, use Drunken Rage, fetch him with Explosive Cask. Then use Body Slam to slow and dmg, auto-attack, Barrel Roll, autoattack, and if CD allows you use Body Slam and Barrel Roll

If he is close and you not completely sure if you can take him down you can start with Body Slam saving Explosive Cask for finishing, or pushing him away from you, or fetching him into the tower if chasing you.

In teamfights you should allmost never let yourself be targeted. find a good location where you are hard too reach, or stand next to a wall, prepered to Body Slam into safety.
The Explosive Cask is great for using in start of teamfight to set the enemy team of position, or for fetching out the dmg-dealers, and at the same time deal massive dmg. spam Barrel Roll as much as posible. if your team gets the upper hand you can go in and help finishing of with Body Slam and auto attacks.
remember to allway use your Drunken Rage as it reduses the dmg you take alot, and gives you some solid AD, as well as filling your mana.

if your team is pushing one lane and the enemy team is defending, you should always look for an opening too fetch a enemy with Explosive Cask, giving you team valuable kills and good pushing-chanses.

Gragas is a great lanepusher, and with a decent ward set-up you should be able to push lanes quite far on your own, without being in a bit risk of getting caught.

Gragas is a great farmer, and are very item-dependent, so throughout the whole game you should always try to farm alot. In the end you should have one of the biggest farms in the game.