Rammus is systematically the MOST banned champion in ranked games. People just plain hate him. Now, if you're having a bad lose streak, and you just want an easy solo queue victory; Rammus is the champion to play.

I do not claim to be the fountain of knowledge. If you don't want to follow this build, than don't. If you want to follow this to the letter, feel free. This is my first build however, so please don't be harsh. ;) Also, don't stack armor against a caster heavy team. That's just stupid.(: feel free to change the build around.

Key:
Ball=Powerball, You're Q, You're incrediboss escape or initiate.
Curl=Defensive Ball Curl
Taunt/Poke=Puncturing Taunt (The reason people hate you)
Ult=Tremors, your fat AoE which takes out turrets faster than a turbo charged udyr

Powerball

I can't stress how important this ability is. Max it first. This is Rammus' only form of move speed basically, and combined with ghost you're moving like a lightning bolt.

Defensive Ball Curl

This is how Rammus is a massive farmer. Even with a few armor items, you can go next to a creep wave, pop your curl, and auto attack them. They won't be able to damage you, and your damage return will take them out crazy fast (especially with a sunfire)

PUNCTURING TAUNT

Everybody hates you. When the enemy is whaling on your turret with masses of their minions helping them out, just poke em. Before they even know what happened the turret has taken out half their health.

Tremors

Aside from being a sick movie, this is your ult. It's got a pretty short cooldown, and it affects structures, so feel free to pop it when your taking out that tower. at level 3, this is effectively has 3 sunfire stacks for a few seconds.

Armor is the only thing Rammus needs. Straight armor seals. I would get magic penetration next because the damage return on you're ball curl and thornmail are both magic. The Extra CDR just lets you spam your poke even more [:

Armor
That's it.
Maybe some health stuff, but eh.
Start with a doran's shield, because you'll notice the difference early on. I've tried using a cloth armor and a few health pots, but I always ended up doing better with just harassing with my ball curl and walking away and regenerating, and the armor stat is important.
Next is Ninja Tabi (durr)
If you have enough, feel free to just straight rush a sunfire cape, but I usually have to go back before that so I get a chainmail or cloth armor. Next I get a thronmail, so I can start ganking and screwing up their fat attack speed Ashe or Kog'Maw in mid.
Next I go for the atma's with the added armor and health bonus (VERY handy) you should a whole lot beefier once you get this item.
Hit up A randuins next, so if they're starting to escape your powerball slow, just completely nullify their usefullness with its active.
The game (which you just lost) should have really ended by now with either a surrender or extensive rage-quits on the enemy team, but if its still going, feel free to sell your dorans shield and pick up a guardian angel or a banshee veil depending on the enemy team (Guardian = Melee Heavy with fat DPS, Banshee = team with karthus)

Ghost + Powerball = "What, you were attacking me?"
All the other summoner spells are viable really, except Rally and Revive (LOL)
IF you don't find yourself being mana hungry, feel free to pick up teleport or Fortify, or maybe ignite if you're playing offensive.

You should be getting your ninja tabi in this, and start building your sunfire.

PLAYSTYLE

last hit large groups of creeps with your power ball whenever you can, and when the enemy is in your turret range, smack em with your slow and taunt them (They hate you so much)IF you don't feel like pushing super hard go get your red buff when you can, or maybe blue if your team isn't very mana hungry.
Try to start by being in a lane with ranged champion, preferably someone with some CC, but them being ranged is a requirement.

This is the period in which you start to rape. You Should have your thornmail by now, and you should start ganking mid whenever able.
The combo is basically the same, except now that teamfights are starting to happen, you should be initiating for those. Also don't be afraid of using your powerball as an escape machanism. The only thing that can really stop you with this is the Ezreal or Master Yi blink directly in front of you and you hit them, but then they would have been slowed, so pop ball curl and continue to walk away :D

THE OTHER TEAM HATES YOU SOOOOOOOOO MUCH.

You should be taunting their squishy as much as possible, and have your ult up whenever on the offensive. The game is now over. By now you should be taking about 80% reduced physical damage outside of your curl, so if you really want to solo a tower,trade out a guardian/banshee for a warmogs and pop your ball curl as you take that tower. (95% reduced physical damage ftw!?) (:

Play safe early game, last hit minions, piss the other team off and above all enjoy yourself [: (Just make sure you don't get reported!) Please don't vote down without a reason why. I like it when people talk to me[:

(Oh, btw, I made it so you can't vote without commetning:3)