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.
Whenever I have to play a tank I tend to play Rammus. The choice of this is that he's got taunt, slow, AOE, and an ability to raise his defence against magical and physical dmg.
Boots of swiftness - This is to get your speed up in order for FB or to escape enemies.
Health potion x2 - This is to keep you out on the lane longer. Helps in the beginning, but are useless endgame in my opinion.
Chainvest - To get the basic defence against physical damage early on.
Mercury's Treads - To give basic magic resistance and to reduce time being slowed, stunned etc.
Sunfire cape - Gives AOE damage, HP, and Armor. This item is good since ALL champions doesn't go with AP, so you will still have to get your armor up.
Force of nature - Health reg. and magic resistance. I don't think I have to say more than health reg. + magic resistance is always good to have.
Banshee's veil - Magic resistance, HP, mana, and blocks 1 negative spell every 30 sec. Great item to have in order to get successful combat engages.
Guardian angel - Gives armor, and magic resistance. Good to have in case you're in a difficult situation.
1. Defensive Ball Curl(DBC) - I always go with this since it gives me more resistance against incoming damage early in the game.
2. Puncturing Taunt (PT) - This is to keep enemies from running. This ability gives you 1/1.5/2/2.5/3 extra seconds to inflict dmg on the enemy.
3. Powerball (PB) - Slows enemies. I use this more to engage combat than doing damage to the enemy. This will be the last one to max.
4. DBC - Playing as a tank means you'll need your defensive.
5. PT - Combining this with DBC is great which is why I level these abilities first.
6. Tremors - You now got your ulti. This ability can be used to do damage to other player or to help bringing down the turrets faster. If you don't believe me, try it yourself.
14. PB - Lastly I go for PB since now you want to make the enemies slower.
Greater Mark of Warding x9 - To get more magic resistance is great since I see many people play AP-heroes.
Greater Glyph of Warding x9 - Same as above
Greater Seal of Resillience x9 - To get your basic armor up.
Greater Quintessence of Fortitude x3 - More hp at lvl 1 is really good to have if you don't want to be FBd.
How to play:
There are many ways to play Rammus. My way is just one of various ways of playing him. This way of playing works really good for me, but it might not work so well for others.
Since you won't go middle you go either top or bot. Having the Boots of swiftness you should be able to dive into the bushes a bit quicker than the other team. This tactic is common, so if you're in the bush before the enemy you wait for them to enter the bush before you start attacking them, but if they don't enter the bush just wait for ganking opportunity of just an opportunity to attack and inflict loads of damage.
At lvl 1 you don't want to be too aggressive since you don't have any slow ability or taunt. I suggest that you keep away from engaging combat until lvl 2 when you get your taunt.
At lvl 6 go back to buy items. If you've been harassed you can go back earlier, but you should stay out on the lane as long as possible. If you haven't been harassed or anything then you should've been able to farm money on the lane up to lvl 6 which gives you a fair amount of money. Buy chain vest first before completing Mercury's Treads.
After buying you get back to your lane. To save time use PB while in "spawn". This will save you a couple of seconds, and you want those seconds if you're going to gank or protect tower.
While engaging combat the skill sequence is important. I use an sequence I believe is very common when it comes to engaging with rammus.
The skill sequence I use is this: PB->PT->DBC->Tremors.
This might not be the most effective way to engage, but I find it very useful. The reason for tremors being last is that i first want to make sure the enemy/enemies are close before activating it.
I use PT right after PB in order to force the other player to stay while I activate my DBC. Many people might argue that you should activate DBC before PT, but the enemies often tries to flash away. Thus I use PT in order to force them to "return" even if they flash.
If you're lane has destroyed the first enemy tower, go either back to base and buy items or go to another lane. Whenever I play my team will try to take out the towers layer by layer. This will help in endgame to keep putting pressure on them defending the towers. The only time you return to your lane is either when you're going to attack the next "layer" of tower or to defend your own.
Flash + PB - Having flash as a summoner spell is great when you're playing as rammus. With this you can flash past creeps and right into the enemy which is a good way to surprise the enemy.
Flash + PT = Tower Taunt - Tower taunting is something that I see a lot of people get really pissed of at. It's a cowardly way to hurt people, but desperate times calls for desperate measures.