Rammus will be a great Tank but you will do tons of Damage with ur Ultimate too.
He got awesome basic stats and get heavy armor and Magic Resist.
If you will get Full build there arent enough enemys on map to kill you.

I picked Flat Armor Pen Marks because they will give you more armor pen, which will help you in early game by harrassing enemys.
Flat Armor Seals will help in Early and Midgame too..the enemy targets will hate u if they do minimal damage.
And the Level 18 Magic Resist Glyphs will help you against Ap Champs..they all will bite their teeths off..
26 health Quints dont need a description..u will start with more life..so you will be lucky to get more health.

0/26/4 Masteries will give u a great stance and laning domination..Really good Defensive Skills are in these Mastery..test it

Flash and Exhaust will be the best if you play laning Rammus.
Tipp to use flash ur best way...stay in bush press ur Q and wait till u get an high movement speed..roll out of the bush and flash u in the enemys Face...
Exhaust is self explained. U slow the enemys can bind them on u with ur E and ur Lanepartner could kill him.

You dont need last hits, thats why u will buy ggold items.
Your Laning Partner (normally Carry) will get a really good farm.

U just harass the enemys and if they get in tower range bind them so they will get shot down by the tower.

U are an Tank and has du initiate a team fight...roll on..bind them..get ur shield and damage them with Your Ultimate

Thanks for reading my Rammus Guide..
I hope u will enjoy it

Greetz
Craked89 EU West