This is the best way I found to tank with Rammus, constructive criticism and suggestions are always welcome.

A regrowth pendant is good for solo laning(if you have a jungler) or if you dont want to have to recall that much.

Your going to want to get your Heart of Gold next because it is cheap, useful, and it gives you cash for later items.

I find that Mercury Treads are more effective than Ninja Tabi because they allow you to get away from fights easier. Also, if you are using Ninja Tabi and dodge an attack with your Defensive Ball Curl up, you will do less damage.

Thorn Mail is an obvious must for all tanks with massive armor and the passive.

Force of Nature is great for magic resistance and will give you massive health regeneration so you can stay in the field longer.

Randuin's Omen may as well have been made for Rammus.

Warmog's is just health stacking which will compliment your Force of Nature.

You always want to stack your taunt as quick as possible to pull enemies into your team mates and turrets.

Defensive Ball Curl is second because it will be your main source of damage other than your ultimate which has a 60 second cooldown.

Power Ball is last because it is mainly used for transport and initiating fights.

Of course level your ultimate at 6, 11, and 16.

Rammus doesn't benefit from many summoner abilities.

Clarity is good because you will run out of mana after a few fights that you won't lose much HP in.

Cleanse is optional, but I prefer it over Ghost or Flash. All work about the same way.

Overall, try to stick with at least one team mate at all times to do your damage for you.

Preferably lane with a high damage ranged champion.

Tanking turrets is easy with this build, just let your team mates do the work.

Have fun being indestructible!!!!

(>'.')> ^( '.' )^ <('.'<) v( '.' )v (>'.')>