This is a normal tank guide, but with a twist... Revive? Yes, something only rammus can pull off and use well. This build is good, fun, and will often make your opponent yell in all chat "HOLY ****"

For runes, i take armor penetration marks, because rammus is a DPS/Tank because of his passive.
i take mana regen per 18 seals because a rammus with no mana is pretty useless.
i take magic resist per 18 glyphs because rammus isnt very good against magic damage and this helps out.
and finally, i take 3 movement speed 1.5% quints because you're always moving place to place. Some may say this is stupid and you should take something better, but i believe movement speed helps in just about all situations.

For masteries i go 21 in defense and 9 in utility for the gold and experience, nothing special.

For items, i start out with a regrowth pendant, which allows me to farm easier and heal quickly from small fights. when i go back, i get Ninja Tabi for shoes. The armor helps you tank and do more damage while the dodge will help you stay in longer and give you a slight speed boost from time to time do to Nimbleness. Next i take the regrowth pendant and make it into a Eleisa's Miracle. The tenacity is helpful so i dont have to get those expensive mercury treads, while giving me great hp and mana regen so i can stay in fights. Next i build the most important item for rammus, Thornmail. Thornmail gives you 100 armor, so it allows you to tank carrys like nothing and make them kill themselves with the 30% damage back, while it gives you a 25 attack damage boost do to your passive making them have to retreat quickly, saving the lives of your squishies. Next i go either warmogs or force of nature, depending on how ap-heavy the other team is. After those, i usually get Randuins omen or a sunfire cape, either will do.

For skills, i start with 1 point into powerball for moving purposes and slight damage, but i prioritize taunt because it's good for holding them in place and lowering their armor while your lane partner starts mauling them down. Laning with melee carries is usually best for rammus because taunt allows them to do alot more damage while you do your job and tank. Get a point into your ult whenever you can. Max defense curl next, because you can tank like a boss with it on and it also increases your attack so you can do a good chunk of damage back. Finally, max powerball.

Ghost and Revive... Basically, this gives you 2 lives. As soon as you die, you revive, ghost, and then roll back in within 10 seconds and catch them off guard and weak. You can usually pick up 1 or 2 weak enemies with this or save your fleeing teammates.. or if your fight was successful, you can roll and help push with full health.

To sum it all up, You'll be rolling, and they will be hating.

GG