To say in advance, this is my first build and the build I use whenever I play Rammus. I find it to be a very effective build for my play style and I hope it works for all of you as well.
*Note no Jungling tips here. This is not a jungle Rammus guide.*
I turned off requiring a comment to vote. It doesn't help anyway I realize when people just comment. "-1"
Changes: Added tooltips as of late, will be touching up some spots here and there regarding the mana regeneration changes, health runes/masteries, and Doran's shield once I figure out what I like or find useful now.
Also go check out Bguggs's Guide out as well. There's more than enough information on Rammus there on his playstyle/tips & tricks to help out anyone new to this character. It's very well written, I just don't like most of his item builds. :D (( http://www.mobafire.com/league-of-legends/build/bguggss-guide-to-the-competitive-rammus-53602 ))
Primarily for Rammus I prefer to use Ghost and Flash over other things like Teleport, Exhaust, Ignite, or Heal.
Ghost seems ideal to me because as Rammus, I find myself often having to chase one or more players down for my team, allowing Ghost to act as sort of a second powerball or enhancing an active powerball move.
Flash is particularly useful as well because it allows Rammus to get in the right position much easier than it would be to just path there normally. For a few examples, I use flash to skip over minions protecting an enemy from being powerballed, to jump to a target I need to taunt that second (Usually to break the cast time of an ability or save an ally), or to flash away from battle and powerball home when my health is looking terribly low.
Teleport can be a useful spell to use in place of any of the two above, allowing you to be a bit of a multi-lane tanker in early game fights. Late game it becomes more useful as you can tank for a team fight then recall, heal up, teleport back in, and tank once again in a matter of ten to fifteen seconds. It's also particularly useful because it allows you to move around the map more freely without worrying about missing a team fight (for the most part). As long as you have something to teleport in on, it's all good.
Exhaust is probably the only other spell next to the above three I'd carry around normally. This is a great spell in particular to keep a second dps player on the enemy team slightly controlled for a few seconds while you have another target taunted and/or slowed. I find this to be more of a spell you would carry for your team over yourself.
Heal...well...it's healing of course, healing is always good in a pinch~! Though it may be good, it's not always the most effective or efficient spell to use in combination with this character. I don't say it's a bad thing to use if you do like using heal, but I'm saying you might benefit your team more by carrying other spells.
This set up for your Masteries quite compliments my Ghost and Flash set up because of the two points into their select upgrades. This build overall though focuses on three primary details.
Veteran scars -- +48 health
Hardiness/Resistance -- +6 to Armor/Magic Res.
And Meditation -- +3 Mana per 5 (I believe it is now.)
The first two, in combination with my rune set up, usually means I can tank more than enough for early game laning. The extra mana regeneration is very nice to have as well as it encourages and allows you to use more abilities throughout the game.
I think this is a pretty standard skill sequence to use for Rammus because his Puncturing Taunt is amazing, some might say even OP~! Maximizing taunt first is always helpful because you can pull enemies into towers with it, prevent them from using spells, and keep them away from an ally.
Defensive Ball Curl is also what helps Rammus do what he does best, tank. It adds 50 + (25 per additional rank) to both his armor and magic resistance temporarily. It also is very nice to use because of it's retaliation effect, causing attackers to take a set amount of damage back based on the current amount of armor you have. *As a note I highly doubt the armor gained from this effect adds into the damage reflected*
Powerball, just keep on spinning. Powerball is quite obviously great for getting from point A to point B very quickly, adding a little bit of damage and a slow in if point B happens to be an enemy. The slow effect on hit is handy for keeping up with targets for a few seconds before having to taunt them in place. On hit, powerball also knocks the target just an inch away, breaking channeled moves and acting as a way to nudge them twards your allies. If I can Puncturing Taunt an opponent first, I'll save Powerball until it wears out just so I can keep them knocked in place for another half second from the impact and have them slowed afterwards.
Tremors, a small but effective area of effect damage spell. This spell is probably the best way for Rammus to get any good farming done next to Defensive ball. It's relatively short cooldown makes this spell quite handy to use for nearly all combat situations: big minon hordes, team battles, one on one, or even going for tougher neutral minion's/dragon, it's a wonderful ultimate to have for everything but tanks, it won't do too much there.
While making this build, I tried to figure out what combination of items will keep me in a position to tank. As I played more, I found that having regeneration early game, focusing health mid-game, and resistance/armor late game, seemed to be the most effective way to go about things as a tank for me. (Results may vary of course)
Starting with a Regrowth Pendant and Health potion from the start is helpful during the laning phase, allowing some of that regeneration early game while being good for the Philosopher's Stone (Added Regen with Mana Regen and Gold) to grab during your first recall.
>>> Alternatively, if this doesn't appeal to your preferences, then I'd recommend equipping your Seals of Clarity before starting off with a Doran's Shield. This should pull you through the early game and allow you to get Boots of Speed and a Heart of Gold just a tad sooner. <<<
Getting Boots of Speed along with either a Heart of Gold or a Warden's Mail will help keep things somewhat manageable in the early game. If you have a lane with lots of casters, feel free to push any of the magic resistance items earlier on or stick to this build order and keep defensive ball up when moving into their harassment range.
For the next part, grabbing a Null-Magic Mantle gives just enough resistance for a little while, building up later into the Mercury's Treads which is so very helpful at reducing CC effects. Now because I'm a bit of a greedy player, I put off grabbing Randuin's Omen for just a little longer, hoping to milk the Heart of Gold's passive for a few more minutes.
After that, I tend to focus on maximizing Rammus's health as high as I can get for the mid-game since having a few more ranks in Defensive ball will cover not going for armor/resistance. About this time I get the Catalyst the Protector first before grabbing a Giant's Belt after.
Transitioning into more of a late game, you can take whatever path you want if you need more armor/damage first ( Sunfire Cape) or some Magic resistance and a spell sheild ( Banshee's Veil).
If the game gets longer, this is the point where I'd usually grab a Force of Nature for the magic resist and health regeneration with the extra movement speed thrown in. If there's some really high physical DPS on the enemy team, however, I'll gladly take a Thornmail to reflect some damage back at them, buffing Defensive ball's retaliation as well.
Beyond that, feel free to sell the Philosopher's Stone for the item you didn't choose at the end or anything else you feel like getting. ( Atma's Impaler perhaps *Shrugs*)
((If you get a team of nearly all melee characters, roughly 4 or 5 in 5v5's, then definitely push Thornmail forward in front of the Banshee's Veil gear.))
Playing a Tank Rammus, you primarily should try your best to keep any of your squishier team mates from being focused down as much as you can obviously. Use Taunt to keep key enemies from using abilities that could devastate your team like Fiddlestick's ultimate for example. Taunt is also great for getting enemies in position for your teammates or keeping them where they are. (It's fun to center targets in the middle of Pantheon's ultimate.) On another note, it's best to focus down fed enemy players! Take the damage from them for your team!
I believe that sums everything up.
Tell me if this is helpful for you or not down in the comments.
Feel free to also add constructive criticism down in the comments as well.
^_^ Have fun ^_^
Edit: Thanks so much for all the positive feedback and constructive criticism I have gotten so far., it has all helped so much. :)