Welcome to my first guide! As you can plainly see, this is a guide for Rammus. Also take note that this guide completely focuses on ARAM! I have been playing a lot of ARAM on PBE (the actual playlist/queue). I have not played a single game of Rammus in a normal 5v5 so please do not base anything I say for that. I have a lot of fun in ARAM but I try to win at the same time. My team usually ends up with no tank, or our tank didn't peel. So I decided to do something about it, and this was my solution :D

For the masteries I just went straight 30 into defense. Since I'm slapping so much armor onto this build, I think the legendary armor points are well invested. The rest is for keeping you alive, or for longer at least. Pretty self explanatory. If you take ghost, ignite, or any other summoner spells, you should consider putting a point into the corresponding mastery.

Here I take all armor/magic resist runes. Rammus gets AD from his passive, and a lot of it with this build, so I see no need for other runes. Since this is ARAM I highly recommend the scaling runes over flats. Flats will work fine though, and can make the first level 3 fight hilarious when their AD's poke you for next to nothing.

Personally I like to rush the Thornmail because I find it funny. Honestly there's no wrong or bad way for the purchase order as long as you're finishing the items. If you're getting slowly killed by the carries but your teammates are still profiting, then keep building what you're building. If you peel some of their carries and your team still dies, go for the Aegis/Bulwark. If AP bursts you down before you can even help your team, switch to a heavier MR build. And lastly, if you're getting slowly killed again, but your team is getting no kills, then get a new team (lol).

To sum everything up, a great defense can make a great offense. This builds job is to be the first one into the teamfight. You'll be able to tank TONS OF DAMAGE and possibly still be alive when you hear the announcer say "Ace". Partly into the game once you have some items, you can easily powerball through turrets to clean up kills if you want. It's risky but really fun and can end in your favor too.

Hopefully this guide ends up being helpful to somebody. Even if you aren't a great player, you can actually help your team by getting beaten up with this guide, and Rammus in general. Just don't try to go in alone if your team is dead :)