Against an AD team comp you just get thornmail-frozen heart-glory-GA and then run it down mid, b/c when they attack you they will kill themselves, with your ult on so u can kill towers
but what do you do if the enemy team is mostly AP or have a lot of true damage, like vayne how to play and build
You don't play rammus into full ap.
True Damage is rough you just dont really counter that other then ccing them bcuz ur a tank, but AP you build the (not many) MR Items in the game if its like 4 ap or 1 ad or 3 ad 2 ad you basically build spirit visage, all that jazz
Against full AP, you get health and MR. You won't be as damaging, but your taunt is crippling to mages and few mages can reliably kill a tank.
Against true-damage heavy teams, you built Frozen Heart and Thornmail/Randuin's, then build HP. Every true damage oriented champion either will struggle against high HP targets or against AS slows. You can't mindlessly win, but you still can do quite a lot.
Also, for the love of god, pick up tabis against Yi and Vayne. They have a lot of true damage, yes. They're also still fucking AA-reliant champions. They still do significant damage from their autos.
Against full HP, build some MR. Abyssal Mask + Adaptive Helm + Mercury Treads are probably your best bet in most situations. Gargoyles Stoneplate is really good too if you can time it well, as it absorbs the bulk of most burst easily. Then build damage. Thornmail (or at least Bramble Vest), Wits End, Liandry's Torment are all good choices. You don't need as much defensive itemization against a full AP team. As long as you can survive the initial burst, you can survive the rest of the fight pretty easily, so you can spend more on offensive itemization.
I'm not sure what constitutes a "true damage" team, but the true damage champions I struggle against are:
Olaf: Run from Olaf. Assuming you don't have a massive gold / level lead, Olaf just eats you at pretty much all points of the game. You're never able to 1v1 him, so don't bother trying. In teamfights, you'll want to try to peel him off of your carry. While his ult is active all you can really do is stick close to mess with his pathing and try to eat some of his spells for your carry. If your carry is alive when it wears off, then your taunt / powerball / ult slow should pin him in place long enough to kill him.
Darius: You need Bramble to fight him. You'll never win a duel but he'll never catch you either. If your top laner has DPS you can kill him fairly easily. Otherwise, stay away as there's no winning there.
Vayne: Bad Vaynes are just like any other ADC. You roll in, taunt, and she dies. If it's a good Vayne, she'll condemn you every time, so you need to either roll in really fast to make yourself hard to click or flash on top of her, then taunt, and she dies. If she's smart she'll eventually have QSS, so when that happens you'll need to close the distance again after she uses it. Depending on the state of the game this simply may not be possible, so when she uses QSS and condemns you just walk away until powerball is back up and try again. Up until 20-25 minutes, or until she gets very fed, you can 1v1 Vayne. If her team is good at peeling though, you're going to have a tough time and you'll need to play defensively.
Against an AD team comp you just get thornmail-frozen heart-glory-GA and then run it down mid, b/c when they attack you they will kill themselves, with your ult on so u can kill towers
but what do you do if the enemy team is mostly AP or have a lot of true damage, like vayne how to play and build
I know people tell you not to play him into full AP but that's not always avoidable discounting dodging.
Personally when I play rammus into an AP heavy or full AP team, I go with an AP on-hit build because rammus does have a built-in on-hit damage mechanic.
(not necessarily in this order)
So you'll have all of Rammus' normal abilities+
Just under 3000 health 230 MR 1.86 Attack Speed 40% CDR 89 AP 461 movement speed Lifesteal from Wit's End. %health damage from bloodrazor
When I'm in this position I use
Conqueror, Triumph, Legend: Tenacity, Last Stand Nullifying Orb, Celerity
So you have a good amount of sustain, good movement speed, good magic resist, and your auto-attacks will do in the neighborhood of 300 each. It isn't ideal I'll grant you but it seems to be able to get me through those games being useful to my team and not a walking bag of gold.
While I haven't tried it yet, you could make the case to replace the Spirit Visage for a Rageblade, but I like the increased MR more.
You pick Mundo or Galio into AP team comps. they are the anti ap tanks.
As for vs Vayne you deal with her the same way you do Yi.
Be a nuisance and force her to switch targets. the less she can sit on 1 target and proc W the better.
You need to remember she is 100% single target bound for her damage.
