Rammus is I believe the strongest tank in the game. You have to make sure that you know who the enemy champions are so that you can better calculate that amount of armor/magic resistance you will need. If you see that you are getting mostly assist and not kills don't worry because Rammus is more of a run in and take all the damage while your team kills everyone kind of guy.
most of your kills will be from your powerball attack. If a team mate is in trouble or chasing down and enemy or just fighting powerball in and kill its simple.

For runes u don't really need them but it helps just a little. Remember that Rammus need4 things armor,health,magic resistance, and ability power. Yes ability power see Rammus powerball is your top ability and you will find use for it all the time so that harder you hit with it the easier it is to get kills.

Ok for me I like to start of with a Doran's Shield just for the defence it gives at the beginning of the game. Never lane mid or lane by yourself you will probably get killed or not be able to hold the turret. If you can solo a lane your self with Rammus you eather have a sucky enemy or your a God and should tell me how to do this. what you want to do is have your and your team mate rush the grass and turn on def ball curl first run in and drive them out or if your lucky you will get a kill. if you do get a kill run back and buy health pots and mana pots you will need them once you get to lvl 2 and get a power ball you will own just drive them back and then go hide wait for the gank and then powerball in then def ball curl and attack the weakest one for the kill then run and heal with pots u should have like 2 or 3 kills by lvl 8. You get the Aegis just for the support from other people with magic spells. Then the thornmail and sunfire are for the def so that by the end of the match you can lead a push and take out a turret by yourself with the other team attacking you.

Remember your powerball is your power. use it for escape for attack and for stealing kills from your teams :p. Remeber that the ghost give us 32% more movement so if you combine your power ball with that nothing in the world can catch you and nothing can get away from you. Also remember that the powerball only hits if the enemy is in your way u can't directly click on an enemy to hit them u have to click just beyond them. also remember if you have to run Rammus is fast and all you need is your Def ball curl on and even the whole team will not be able to take you out as long as that is on us will be safe. Also the taunt can be use for leading an enemy out of there teams space and into yours. You can literaly run up to and enemy behind a turret and lead them away from the turret and back to your waiting team for the gank. Your ult can hit turrets its the only ult in the game that can so use it will. I would sugest that you only use it to eather hit turrets or run in and save team mates

PROS:
1. Rammus is a great tank for anything.
2. Rammus powerball gives him a great escape tool and a chase tool.
3. Rammus has masive amounts of health.
4. Rammus ult is the only one that can hit turrets.
5. Rammus can take turret hits in the beginning of the game


CONS:
1. Rammus has no long range attacks
2. Rammus will usually be targeted first
3. Rammus is not great at lvling up so it takes some time to get him to full power
4. Rammus does not get alot of kills so don't try

For team work with Rammus you mostly want to ether put him in the lead in a team battle or wait in the bushes and powerball in for the gank. Its a Good thing to powerball in then use your exaught spell. Because of the tremors ult you will find that Rammus is a great support Champion and usually gets anywere from 20 to 30 assist depends on how the match goes in the beginning.