See, I only like about 50 percent of the time guys! <.<
Well, I left off in lane phase, not really discussing any specific item builds. One reason for this is that the way I play Rammus, items aren't as key as they are with other chars. Your characters disruption capacity is what makes you so valuable, and really, survivability is almost never a concern until late, late game. Normally, though, I start off with a heart of gold, even though it was nerfed, and from there, you build according to the situation.
Does the enemy team have a lot of attack speed heroes or escape mechanics? Turn that HOG into a Randuin's Omen and watch that strategy go to shit. If you are lucky, they will be heavy attack damage, in which case you can build a Sunfire Cape first, into a thornmail and laugh as they kill themselves on you (also works against AS teams, but Randuin's tend to help more because it doesn't rely on the opposite attacking you, which they won't unless they are retarded).These builds tend to be great for Rammus, being that his passive gives him damage based on his armor, but what if the opposing team is heavy AP? Well, this is where most Rammus players run into deep shit, as they get this idea that they are supposed to be some super melee damage champion stacking armor. If the other team is heavy AP, once you get your HOG, get your merc treads, build into a Banshees, and then maybe into a Randuin's if you have time.
You may notice that these builds are really light on items. Well that is because Rammus, honestly, sucks at farming. He is almost poppy level shit farming. The problem is building multiple gold generating items, like Phil stone, tends to suck on him because the HOG nerf made stacking them mediocre, at best, and phil stone doesn't build into anything useful. Now, with the new items dropping this next patch, this might change, but I doubt it considering that merc treads will still stay Rammus' boots of choice, being that powerball really is all the movement speed he needs, attack speed is shit on him, and cooldown reduction is okay.
Basically, as far as items are concerned, build against whatever the enemy team is building up, keep randuins in your back pocket, and focus on enemy carry disruption, and you should do fine. Oh, and if you are doing your job, you will die. Terribly. The enemy champs will blow their DPS loads all over your tanky body and while you team pushes for the win, you will have plenty of time to run down after the ace to get a victory beer.
Late game teamfight strategy, in an ideal situation, is very straightforward. You powerball into the enemy team, hitting as many as you can, drop defense ball curl FAST, and use your Ult, finding the nearest carry (AD preferred) and taunting them. Then, you save your powerball if they have any channeled ults (other than nunus), and if they dont', you keep powerballing to reduce movement speed(saving your ally champs 90 percent of the time as they run and kite) and keep the AOE damage going. When it comes to fighting under a turret, I don't recommend diving the turret unless your team has at least a slight advantage in char composition or item builds. Instead, try to bait the enemy team out a little bit, and if you have a stun, have them stun the enemy champ as they get close to the edge of their tower range to harass you. Then, taunt that player, and drag them out of the turret. Whenever this happens, as long as you don't grab a tank, it basically gurantees a team fight win for you, or at least a free baron.
That pretty much concludes this guide. If you have any questions or comments, leave them and I will respond. Hopefully, I didn't miss anything too obvious,.....