Hey! This is my first guide I've made for my favorite tank character, Rammus. Keep in mind that tanks are meant to lead the team into battle and take the most damage from the enemy while not necessarily dealing the most damage. It's about winning the game, not getting the most kills.

If there is anything that you feel I should add or look into feel free to comment.

Ravaged by Rune Wars long past, the lands south of the Great Barrier are wrecked by chaotic magical storms, leaving the grasp of nature's rule tenuous at best. While abnormal flora or fauna are the norm rather than the exception in these ruined areas, perhaps none is more curious than the case of Rammus. While no one is entirely certain why an armadillo from the Shurima Desert crossed the ***ungu Jungle into the Plague Jungles, Rammus made just such a journey. There, amongst the twisted vines and festering rot, he came across an oddity - a healthy evergreen hedge maze, stretching as far as the eye could see. As he explored the maze, something compelled him towards its center - a light, a presence of some kind. As he drew closer, the light surged, blinding him and knocking him unconscious.

When he awoke, Rammus' whole world had changed. The maze had vanished and he felt truly cognizant for the first time in his otherwise unremarkable life. As his predicament dawned on him, Rammus had a moment of panic. As he trembled, the earth around him began to shake, the intensity increasing until he managed to steady himself. As the quake receded, Rammus arose and left the Plague Jungles in search of others like him. His search brought him across all the lands south of the Great Barrier, but everywhere he went, he was unique. The hardships of this sojourn inspired him to craft the suit of armor that would earn him the title of Armordillo. Rammus's quest eventually drew him to the only place where a sentient armadillo is less than confounding - the League of Legends.

"I've seen a lot of things, but this... this is a first." -- Ezreal, the Prodigal

Pros:

-An excellent carry
-Can take massive damage
-Great initiator
-Extremely powerful skill combo
-Slow can help your team catch up to runners
-Ultimate damages turrets as well as minions and Champions
-More armor gives you more attack damage

Cons:

-Short range of attack
-Low mana cap
-Without armor you are just about no help to your team

There are a lot more Pros than there are Cons to playing Rammus. He can really make or break a game.

Do's:

Ignite, a favorite of many players, is a great finisher to get a kill on a Champion that is running away.
Flash can be a great spell to initiate or get away with in addition to Powerball.

Maybe's:

Cleanse can get rid of CC placed on you by the enemy team so that you can continue fighting or escaping.
Fortify can hold enemies off of your turrets for a few seconds. This usually won't work as well later in the game if most of your team is missing from that lane.
Ghost, although in my opinion not as "OMG WTF WHERE DID YOU COME FROM?!?!?" as Flash, can help chase runners or escape.

Dont's:

Everything else. They're really just a waste for Rammus.

Spiked Shell is your passive. It is why Rammus must have armor to dish out some nice attack damage and why I will always use Defensive Ball Curl to get an armor boost to do some more damage to turrets.

Powerball should be your first skill. It will get you to your lane faster so you can wait and hide in a bush. You should max this out last as what you want from it is the speed boost, which does not scale.

Defensive Ball Curl is your second skill. It will give you a huge armor and magic resistance boost as well as deal back some damage. This should be the first skill you max out.

Puncturing Taunt Puncturing Taunt is your third skill. It will make an enemy focus on you with normal attacks for the duration. This should be the second skill you max out. Remember that it can cancel Champion's channeling skills, such as Nunu & Willump's, Miss Fortune's, and Katarina's ultimates.

Tremors is your ultimate, and can be used in many ways. You should get this whenever you can (levels 6, 11, and 16). Because of it's short cooldown (1 minute), you can use it to farm minions. When in a team fight, use this and make sure to stay in range of most of the other team. One amazing thing about Tremmors is that it does damage to turrets. Remember to use that to your advantage, but make sure you have enough armor to do so if the other team is within range of it because the turret will focus you when you deal damage to them.

When I initiate an enemy, I like to come in with a well-placed Powerball. If there is something in the way, such as a few minions, or they start running away and your team can't catch up, Flash to the middle of the enemy after Powerball is on (remember that if you wait a few seconds while in Powerball, your speed will be dramatically increased to come out so that the enemy team won't have enough time or speed to get away). This will cause the enemy team to pop up in the air and be slowed for a few seconds. Then get your Puncturing Taunt on, preferably, a DPS or squishy. As soon as you land that, put up your Defensive Ball Curl and Soaring Slam. This is a great way to initiate as you will be focused first, deal damage to everyone attacking you, and also get your team to deal damage to whoever you decide to focus.

There are a few ways to go as far as items are concerned, but you should usually have the same end items.
To start out, always buy Boots, 2 Health Potion, and a Mana Potion. I go with boots of speed because I first like to know who I'm laning against before I get either armor or magic resistance. The health potions will keep you in the lane longer, and a mana potion will keep your mana up in case you need it.
If the other team is primarily attack damage, your next item is Ninja Tabi. If they are mostly casters, get Mercury's Treads.
If you are laning against physical damage or both physical damage and a caster, you should be getting Sunfire Aegis. If they are casters, buy Force of Nature (I like to start with Regrowth Pendant, but it's a mater of preference). After that, get the other. Sunfire Aegis is your farming tool as well as armor and health while Force of Nature is your health regen and magic resistance (even if you don't need it, the health regen is amazing).
From here on out should be a lot of team fights. If you are taking a lot of physical damage, get Thornmail. If not, get Guardian Angel. After you get one, get the other. Thornmail gives you a lot of armor to tank the turrets (coupled with Defensive Ball Curl for maximum damage mitigation) and Guardian Angel gives you a bit of armor, magic resistance, and somewhat another life to stay in the battle longer.
Warmog's Armor should be your last item. It will give you more health, more health regen, and improve your Force of Nature's passive health regen.

No matter how good Spiked Shell is with armor, you should never go pure armor. You need to know how armor (and magic resistance for that matter) scales and when enough is enough. 315 is plenty, blocking 75% physical damage without your Defensive Ball Curl. It takes about 130 more armor ( Thornmail and some of another item) to get up to 80%, which isn't worth it. Straight up armor won't save you from the casters who will rip you to shreds without your Defensive Ball Curl, nor will that 5% make more of an impact and keep you alive longer than getting health/health regen items. Many Rammus players think you should go pure armor for the extra damage it will give you with Spiked Shell, but your job is to tank, not deal damage. Even if you were to get that extra 130 armor, it will only give you a bonus 32.5 damage, which, if you think about it, isn't as good as being able to regen health as your attack speed is slow.