Hello, I'm going to show you how to set a "complete tank Rammus", vs ad and ap Champs.
In this way you can use Rammus vs every team.
I will speak of his rune, of his spells, of his masteries, of his skill and Item and I give a reason to my choices.
We will observe together merits and defects of that pg and I will explain the rammus use in a teamfight.

Runes

I select these Runes to have much Defense
and Magic Resistance, especially in early game.
Most of all I focus on Defense, 'cause Minions and Champ's basic attacks cause the most of damage.
I pick the Runes of Magic Resistance, 'cause some Champs (like Ryze, Veigar, Fiddlesticks....) cause a lot of damage with skills, even in early game.

Masteries

I choose Masteries that give me Defense, Magic Resistance, HP and Reduced Damage Taken by Minions and Champs. Siege Commander is really useful to demolish Towers, when I tank them. Improved Recallis really understimate, but it saved me a lot of time, for example after destroying a tower and the hole team try to catch me in the brush. Summoner's Resolve and Summoner's Wrathincrease the Spells I choose, Heal and Ghost.

Spells

I use Heal, 'cause recover a few HP, for a tank, during teamfights, helps you to survive enough to allow your allies to kill enemies.
I use Ghostwith Powerballto be fast when I escape and when I chase.

Skill

The skill sequence gives Ramus the possibility to have max Defensive Ball Curlat level 9 which makes it excellent to tank.
In thiss build I give precedence to Defensive Ball Curl and Pungturing Taunt, because ramus is set to tank soon in the game and the Taunt is fundamental to save your Team during the clash.
I take Tremorsat level 6 but not at level 11, because for me Curl and Tunt are more important for thiss pg.

Items

In my Build, I take only armor, magic resist, and Hp.
Because I want tank every pg.
-I select in a first time the shoes, because I like move fast.
-The guardian angel is essential fore 2 cause:
1-It give to me armor and magic resistin a single item.
2-I have the chance to resurrect
-The Thornmail give me armor and allows me to return damage.
Other items increase just magic resist, armor and Hp.
The Banshee's Veil give me protection first skill, such as those genereting taunt or stun and help me to tank the enemy

Merits

-Rammus holding attacks fisical and magic.
-Rammus converts the defense in attacksdamage.
-Rammus hold the enemies forcing to attack and return part of damage taken whit Thornmail and the Defencive Ball Curl.(suicide the enemy °_°).
-Rammus destroys enemy towers in a short time and whitout the need of the Minion.(He Don't take damage when He have a build complete).
-Rammus is one of must faster champs of the game.
-Rammus is power both in 1 vs 1 than in 5 vs 5, because is a tank for a team but able to kill even.

Defects

-Rammus have 1 weakness...another rammus stronger than you.
-Armor penetration and attack spead high can generate some problem.

Rammus does not have an enemy it's kill every time, but every Pg that are constructed whit armor penetration or magic penetration can generate any problem.

But the top enemies of rammus is his team,because many people,not knowing the capabilities, when he tank more pg,they run away.
when using a rammus you must be sure that his team is ready to follow.
because 5 vs 1 is too much even for him :)

Rammus play whell in line with full damage Champs [MasterY for exemple].
Whit a mastery ramus as the possibility to tank each tower or champs also to start, if he is well set.

Rammus in a team is a center of the action.
Ramus jungler isn't usualless but he's harmful for the team, because in a team there is the need to one champ tank.
If Ramus jungler will not be able to tank,at the right time.
The jungle is for the killers or ganker...not for a tank..."the realy tank".
Advoce to all to use Rammuse in line.