Hey community! Thanks for coming to my first build. I'm not about to get deep into backstory but I'll have you know I've played Gragas from summoner levels 1-30 on my first profile.
FYI this is a 3v3 build that would be best if laning solo. If you must lane with another person it would be best if they were heavy damage or had snare or stun. Also it is very tanky and can carry if the game carries on long enough to get all of the items.
SO lets get right into it.

Pros
1. Great pusher/tank
2. Extremely abusive
3. Fantastic support champion.

Cons
1. Squishy beyond belief
2. Slow on EXP gain.
3. Gives you a God Complex

You may notice the runes seem a little health heavy, but that's what makes Gragas good; his overwhelming amount of health. While Gragas is level 8 (or lower if you are starting off well) and below he is very squishy and highly susceptible to ganks, so what I am focusing on is health with a bit of AP so that initial ganking is statistically more successful. This setup is solely made for Gragas' squishiness to be reduced, feel free to modify these as you please but I do recommend having some health benefit to start with.

For masteries you can see we have gone with defense, but not completely. There are a few bonus's in the defensive tree that are irrelevant to Gragas seeing you can still fill the tree and have some left over to reduce your cool-downs, which is a great benefit for tank Gragas. Make sure if you are using the same summoner spells (which I highly recommend) you select them in the masteries. If you want different spells (such as blink instead of ghost) go for it. We'll get into that more later.
You want to go with as little damage taken as possible with a whole bunch of health, making Gragas almost invincible.

Now onto the part that makes Gragas such a decisive part of any match; the item build. We all know that you should build according to your enemies but what I have laid out here is a build for a match where you start off dominating and are pushing strong. Ideally you will have your Warmogs armor by level 8 if you are soloing. You are always going to want the boots of swiftness and the Warmogs armor but if you are facing a caster you will most likely skip the Crystal Scepter and go for either more health with Banshees Veil or go for super AP and get 2 Deathcaps. If you are facing a melee type Yi or WW you would skip the aegis of the legion and go for Thornmail.

Characters such as Teemo and Zilean are somewhat of an issue for Gragas, but I would always take another Deathcap instead of the crystal scepter for those two.

I always start with the ruby crystal for the extra health and start on Warmomgs, it's a great start for ganking. After that if you are doing well enough you can get your giants belt right after (starting the feeling of invincibility), but if your opponents are giving you some trouble, get the boots before continuing the Warmogs chain. From here the items you would like to get are up to you but I always go for the aegis if I'm having trouble pushing a lane, but if business is getting taken care of then I'd say a crystal scepter or begin building a deathcap. The archangels staff is great if you are doing well because your mana will be scare in the beginning (maybe pick up some mana pots if you feel to vulnerable).
At about level 11 with this build Gragas can solo Dragon and Tank turrets (the perfect way to end a game in less than 15:00 minutes). PUSH HARD

This one is pretty basic. Always make your Barrel Roll a priority, and since Drunken rage was nerfed, only get it when you have to, but make sure you get it first at level 2 so you can regenerate some mana. Body slam is a great way to slow your opponents and run away if you need (you can slam through walls), but make sure you level barrel roll whenever you can. As per usual get explosive cask up whenever it is available and you should be okay.

Make sure when you are laning that you don't get to comfortable in the beginning because I cannot stress enough that Gragas is squishy and easy to take advantage of early game. Just play cautious and barrel roll from a distance. Make sure you are killing minions with it as you push easier by doing so (so you can recall safely if you absolutely have to). But overall stay back until you hit level 8-9 then you can force your way through crowds easier while gaining a bunch of money. Also, Don't be expecting a ton of kills early-mid game. Grind and farm for a bit and then tear your way through your opponents.

I can truly say that these two spells have helped me more than anything. They are both great for ganking and getting away. As I've said if you prefer blink instead of ghost you can go for it, but I feel more comfortable with ghost. Gragas is a true train with boots of swiftness and ghost on, it's scary. I usually use exhaust on the initial gank alongside a barrel. It's perfect for taking at least one of them

While you might have picked up on this thus far Gragas will not be doing a lot of killing overall unless the game goes on for a while. Your best bet for teammates are ones who can shave health off of your opponents or ones who can stun or snare. I've found Anivia is an incredible laning partner for Gragas as well as Malzahar and Kassadin. Yi and WW aren't bad if WW isn't jungling. But as I've said before you are going to want to try and solo if your teammates agree. It's in their best interests. TRUST ME. Ask with courtesy please.

So that's about all I have for this build.

Just Remember:
1. Play cautious in the beginning.
2. Utilize the barrel roll as much as you can.
3. About level 8-9 Start pushing hard.
4. Don't get discouraged in the first 15 minutes, Gragas improves significantly late game.
5. GL HF

follow these guidelines and you shall be the tank that is feared all across the world. Enjoy watching Ragequitters every other match. 1v3 late game and get a triple kill.

I hope this helped you Gragas fans. PM me if you have any questions/suggestions/comments. I'd love to hear some feedback and results.