Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
it's my first build, and it's not very different from me others from this site, but this is more to show how a rammus can be a good hero against many kind of teams.
HEAVY DPS TEAM
For this kind of team, you should start with doran's shield, since it gives you a great HP boost and you become from level 1 a though nut to crack. giant's belt, sunfire cape, thornmail, sunfire cape, randuin's omen. The last sunfire cape can be trade for the atma's impaler for the extra demage, but for tanking the 3rd sunfire will work a little better.
HEAVY CASTER TEAM
for a team with casters, it's not Rammus field, but it can be adapted to that situation. first start with mercury's threads, sunfire cape, banshee's veil, sunfire cape, force of nature. The last item can be on of these 3: sunfire cape, warmog's or atma's impaler. this will get you an offensive tank, and can take a good beating from spellers, and do a great deal of damage
for a mixed team, start with mercury's threads, sunfire cape, banshee's veil, sunfire cape, warmog's and for the last item, the same as usual, atma's impaler, sunfire cape or a randuin's omen. i usually take the omen for the hablity cooldown.
you may say that the armor penetration is not the best choice (maybe even the worst) but in early game, rammus have a decent amount of damage, with ignite and exaust, it will help you get an early kill. the HP runes is a no brainer, more life more resistence, just as simple as that. hability cooldown, walways a good thing.
Exaust is very helpfull to get a kill in early game, as well as for tanking, especially vs an Amumu, Sion (to turn that ult rather useless) and every one with Bloodrazor.
Ignite, for that little bit of HP that you didn't manage to take.
This is not an ultimate build. Take in mind that this builds have a major flaw... to take down towers, you will fall a little behind, but that's why atma's impaler is there for =3.
enjoy this build, give it a try, leave comments, im always open to new ideas.