Hello. This is yet another guide by me, and now for the unique turtle, Rammus. Before we move on, I'd like to tell you some things.
Please do not down-vote, flame or do any other negative action just because the cheat sheet is incorrect in your opinion, or lacks anything. I will suggest you make a comment on this, after your have checked the following things:
Please check all the five builds. They all are for different situations, and I'll explain them all later in the guide. Please read that section first.
Read the entire Items section. You might find the answer to your question there.
Read the FAQ, and see if your question might be in there.
If all above is done, feel free to leave a comment. I beg you not to down-vote or do anything else negatively before you have submitted a comment and I've answered you.
This guide is my way of playing Rammus. I'm in no way telling you exactly the best was of playing Rammus. Several sections of this guide will explain the different uses of items in different situations. This is all personal preference.
If there is something you dislike, please tell me so I can eventually correct it, or give you an answer to your question.
When voting, please tell me WHY you up/down-voted. I'd like constructive critism very much, as I'm not a professional guidemaker or player of any kind.
If you have a screenshot of a game you played you think is good, feel free to give me a link in the comments if you want me to add it.
English is not my primary language, and I don't know it too well. There might be a few mistakes here and there, but I'd be really happy if you could comment and tell me where I eventually made the mistakes, for so me to correct them.


Runes, Masteries and the original items in this guide (Yes, there are a big items section handling all the items in all the builds, but...) are after build ONE on the cheat sheet, which is the general build. Of course I will talk about the other builds, but for at least runes and masteries, it's for build one.


With that being said, it's time to move on to the guide. Thank you very much for reading above. "Mhm"


Abbreviations

In case you don't understand a couple of abbreviations I use in this guide, here's a list of commonly used abbreviations:

Abbreviation - Definition
Armor - Armor
MR - Magic Resist
ArmPen - Armor Penetration
MagPen - Magic Penetration
AD - Attack Damage
AS - Attack Speed
AP - Ability Power
Hp5 - Health per 5 seconds
Mp5 - Mana per 5 seconds
CDR - Cooldown Reduction
CC - Crowd Control Effects (Disables)
CS - Creep Score
MS - Movement Speed
tl;dr - Too Long ; Didn't Read
IMO - In My Opinion
TBH - To Be Honest
ASAP - As Soon As Possible
Pull or Leash - Get a teammate to hit the target and go back to lane immediately

Let's get on with the guide, shall we? "Ok".


Pros / Cons | Why Rammus?

SPACE
Pros:
- An exceptional tank
- Easy to play
- Can save people's butts countless times
- Really hard to defeat with Defensive Ball Curl activated
- Is a turtle. Ok. How magnificent. SPACE SPACE
Cons:
- Easy to play yes, but hard to really master
- Tenacity is really annoying
- Very, very often banned in rankeds. At least in the lower ELOs for sure. Probably the most banned champion?
- More vulnerable than other tanks when Defensive Ball Curl is deactivated.

Why Rammus?
Rammus is probably one of the best tanks in game. He has a great taunt that lasts for up to three seconds. This can save your teammates so many times, and I feel so good when I get a "omfg ty rammus<3" in return. He is really easy to play, and you should start getting the holds of him after just a few games. However, he is hard to really master. He is hard to play very good. If you can fully master Rammus, you're the one who can lead your team to victory. With Puncturing Taunt, you can get your carries fed enough to carry the game themself.

Rammus also has an awesome speed boost. You can catch up with escapers, roll away from enemies chasing you, or use it to interrupt channeling spells. I will come back to this later.
There's so many nice things you can say about Rammus. I won't mention everything, or it'd look like a book.

Now, let's get started for real, "ok"?


The Builds

First of all, I will explain the cheat sheet builds.
But before that, I'd like you to know that the builds have a lot of items in them at the end, as the items you would get should really vary on the opposing team.

Build 1:
Build one is the general build. It's how you would build for a decent enemy team, usually consisting of around equal damage output of AD and AP. If the teams gets a little bit more unbalanced, I've added a bunch of other items you can get to satisfy you and your team.

Build 2:
Build two is the general Rammus jungle build. Rammus is a decent jungler, and it's quite easy to do. A video will be added later.
The runes of this build are a bit more specified to your job as a jungler, and so are the early-game items. The rest of the items are around the same as build two. Remember to adjust them after how well the enemies' AD or AP carries are doing.

Build 3:
This build is for if you're facing a very heavy AD team. It contains a bit of MR aswell, however it mainly focuses on getting Armor. Armor will also improve your AD, which is a great bonus. Remember to not always exactly follow this build. If the enemy's AD carry is fed, and you see the AP carry also has picked up a small bunch of kills, it might be smart to a little bit MR. Guardian's Angel should give you MR needed enough though, if the enemy's caster sucks.

Build 4:
The opposite of build three, is build four. This mainly focuses on heavy MR, with a little boost of Armor aswell. Remember that getting some Armor is great for Rammus, due to his passive. However if you find your enemy AP carry with a blowing 30/2/14, it's worth investing some money in a bunch of MR. Remember that the enemy might have an AD carry there too, having a potential damage ouput. Be aware.


General information
Common with all the builds, you will find health items as a key. Why, you ask? Well, as you probably already know, when you start stacking higher Armor and MR, the effects will just decay more and more until you get stuck at round 83%. You can't go much higher if you don't have six Thornmails and activate Defensive Ball Curl I guess. However, this shouldn't be done. You lose too much money.

Here's a nice graph for you:
As you can see, around 400 is the limit. It flattens so much out that... well yes. The cap of Armor/MR you should get before you should stack health, is around 200-300.

Then, the question would be: But I have my Defensive Ball Curl, which gives me +150!!! Shouldn't I then just get 50 Armor and 50 MR then spam Warmogs???

No. Why? Simple. As said in the tips when playing against Rammus, his stats are slightly lower than any other tank when Defensive Ball Curl is deactivated. Along with any other abilities, it has a cooldown. And to cover the room between the cooldown and the activation of this spell we need Armor and MR. A fight will probably last longer than six seconds, and the cooldown of this spell is 14 seconds. That makes you very vulnerable within those eight seconds, and therefore getting Armor and MR is a must, like with any other tank. It's when Defensive Ball Curl is activated Rammus really shines. That's when he is amazing. When it's off, he's like any other tank, except that he is a turtle.

tl;dr
Really? Well, since I'm one of the nice turtles, I'll give you the short story.

Use build one/two for general games. If the opponent team is quite balanced, I'd recommend one of those. Notice that it's up to you what you buy late game though.

If you're facing a heavy AD opponent team, go for build three. It also builds a little MR of course. However if you're facing a strong MR team, go for build four. Build four also builds a bit armor.


Runes

In this section I will be explaining my choice of runes.
Hence that this is for build one.



Marks
Any rune could fit here. Marks doesn't give a good defensive bonus, so you should use what you have. If you have 9x Greater Mark of Fortitude, I'd suggest you use them. If not, anything else. These runes aren't too important for an tank.
Jungle: In the jungle, these runes are great. I'd suggest you to use Greater Mark of Alacrity, Greater Mark of Strength or Greater Mark of Desolation. These are runes that really help you out. Greater Mark of Fortitude is a decent choice aswell, imo.

Note that I don't encourage you to buy 9x Greater Mark of Fortitude. If you have them, they're better than Greater Mark of Insight. If not, go with the Greater Mark of Insight. The health bonus aren't too big, but it is something.

Seals
Seals are probably the most important runes for Rammus. All I can say is Greater Seal of Resilience. Armor, Armor Armor. Rammus gains AD from Armor, and Seals' biggest boost is Armor. You can choose for yourself wheter you want flats or pr.level, but I'd prefer flats myself. This is due to the great help it gives you in the jungle: 1.41 x 9 = 12.69. It gives you a whopping 12 armor bonus in both lane and jungle, and this will be 30 with your cloth armor, along with 6 from masteries which will give you 36. Rammus' base armor is 21, which will reward you in having a sick 57 armor to start off with!!! As you can see on the graph in the previous section, the physical damage dealt to you will be reduced by around 36%!!! This bonus is SICK early game, where spells doesn't do too much damage. Wow. No doubt here.
Jungle: Exactly the same. Insane surviability boost.
Remember that this will add to your AD aswell. 57 armor divided by 4 equals 14. That means an extra 14 AD for you.

Glyphs
As for glyphs, the best for Rammus to get would definitely be Greater Glyph of Warding or Greater Glyph of Shielding. This is really, really up to you, but you want to get MR for sure. Per level might be a good idea though, as these will kick in at level 7, and their effect will be bigger than the flats right there at level 7. By that time, peoples' spells aren't way too strong, and therefore I'd suppose that per levels would be the best.
Personal preference.

Quintessences
Greater Quintessence of Fortitude. Health quints are imo best, but it's up to you what you choose. Quints are good overall, and anything tanky would work. Greater Quintessence of Defence, Greater Quintessence of Warding etc. Nothing really much to say here for sure. It's all up to yourself. I just have to state that starting out with (26 x 3) = 78 more health will really help.
RUNES

Greater Mark of Insight
9
Greater Seal of Resilience
9
Greater Glyph of Shielding
9
Greater Quintessence of Fortitude
3

Now, lets move on to the masteries I've chosen. "Ok".


Masteries

For the general build, the masteries are set as the follows:

MASTERIES
3/3

3/3

4/4

2/2

1/1

3/3

1/3

3/3

1/1

1/1

3/3

1/1

4/4


So, basically this is my personal preferences. Some points can be swapped here and there, and yet today I don't know which is the best. Initiator etc can be very useful, however so is Honor Guard. Mercenary is another decent spell, I mean it will reward you with some good gold if you get 40 assists, huh?

30 assists:
Mercenary level 1: 240g
Mercenary level 2: 480g
Mercenary level 3: 720g

720g is something, and for only three mastery points. However, again, Veteran's Scars requires 5 mastery points, and so it goes on... It's up to you to decide, and just putting 30 points in there somewhere will make great difference :)

The rest is pretty much basic tank masteries, 0-21-9.

The jungle build isn't really very different;

MASTERIES
1/1

3/3

3/3

2/2

4/4

2/2

1/1

1/1

3/3

1/1

1/1

3/3

4/4

1/1


Again, it's a wide selection of alternatives. Summoner's Resolve will grant you some bonus gold throughout the game, just like Mercenary again, as explained above. A very very useful mastery point for any jungler is the Runic Affinity. 20% longer buff duration is gold! Swiftness is good for moving faster... everywhere. The point placed in Summoner's Insight is for your Flash.
- Keep in mind that Initiator can be incredibly useful in some situations.

Rammus Jungle is now much better than before!
- Why is that?
Due to the new mastery, Bladed Armor. This stacks up with your Defensive Ball Curl, and will make a sweet difference. Your jungling will go faster, and all the red wraiths will now die while you attack the blue. (Well, you're probably too fast so you gotta auto-attack them anyway :)). Tough Skin and Indomitable will protect you nicely, granting you more surviability in the jungle.

A good choice for almost any jungler is Butcher. Some, like Rammus and Amumu are tanks, and will have much more benefits from the Defense Tree.


Items

For the item section, I'm going to talk about the general build and the jungle build. The two others are very situational, and I will also explain situational items; when and where to get them.

STARTING ITEMS


General: Regrowth Pendant, Health Potion
Physical: Cloth Armor, 5x Health Potion or 3x Health Potion and 2x Mana Potion
Magical: Null-Magic Mantle, 2x Health Potion

Make your support cv their base 5-15 sec after start.



General Build (#1)(#2)
- Regrowth Pendant
This item will give you extreme sustainability in the lane, aswell as later on build into Philosopher's Stone. It's amazing to have, and can let you stay in lane basically forever, as long as you don't risk too much. With your Defensive Ball Curl, this will make you never ever need to go back. I'm not telling you to NOT go back. No.

- Philosopher's Stone
Built from your starting item, this item is to be got early on. It'll reward you with 5 gold per 10 seconds, which will reward you in getting 30/1min, 300 gold each 10 minutes you have it. Keep it for 30 minutes and it'll give you more than it costed - and that's when you sell it. You only need the hp regen and mana regen on your way in the early game phase.

- Heart of Gold
Another gold per 5 item, which also gives you a small HP boost in the laning phase - sweet! Another sustainability item, great to have! With both this and your Philosopher's Stone, the amount of gold you gain per second is almost doubled! Wow. This item, however, won't be sold. It should build into Randuin's Omen later on.

- Mercury's Treads or Ninja Tabi
It's up to your opponents what you get. I'd like to get Mercury's Treads if they have 5+ strong cc's (stun, suppress, taunt) or like 6-7+ cc's including slow. I also get them if the opponent team is balanced AND have 3+ cc's. If you're facing a heavy AD team, or just heavily fed, and barely (5-) cc's, I'd go for Ninja Tabi.

- Guardian Angel
A great item which gives both Armor and MR, along with an amazing passive! This item tends to be gotten in late game, however getting it before is actually very rewarding. It's passive will always be 750 HP and 375 Mana, which will be worth more early game than late game! Therefore I use to get it earlier on, but it's all up to yourself. Before this, I do grab a Giant's Belt to get another small boost of HP on the way though.

- Sunfire Cape
Nice item, both armor and HP! A sweet passive, and doesn't cost way too much. I'd say its a nice item to get.
Note: If you need to sell an item, this is the one I'd go for. E.g. if you face a very heavy AD team and want to buy another Thornmail or so. This is the one I'd sell.

- Randuin's Omen
This item will give you an AOE slow to both attack and movement speeds, and if you use this while your Defensive Ball Curl is activated, it has an amazingly longer effect. This is built from your earlier gotten item, Heart of Gold.

- Warmog's Armor
Crazy HP boost. With the kind of ""minor"" stats you've gotten so far (not really HUGE boost - items), it will help great together with your Defensive Ball Curl. This is where you get at the point that HP items is worth more of your money than getting Armor/MR.
Note: This item can be extended and bought later instead.