this build is my personal build, like it or not.
as a normal jungler, i take cloth armour + 5 health potions.
After first teleport, i take boots, and if possible, finish them in first teleport.
The reason i take a fast guardian angel is because i see rammus as a tank, who roll into the middle, and always start a team fight. And if all goes well, Rammus will be targeted, and then saved by guardian angel.
Rammus are an armour tank, his armour buffs his ad, so thornmail is a good choice for Rammus. + if you use your "W" with thornmail, the enemies will kill themself instead of you.
Sunfire cape is for the hp, meaby rammus are an armour tank, but all tanks need hp.
frozen heart is for reducing the enemies attack speed, and for some armour.
The last item for Rammus are depending on the teams, if your enemies have alot of cc, buy banshees veil. if the enemies have alot ap based champs, get force of nature.

Here are some tips for the jungle:
start with blue buff, try get someone to push for you. (remember only to use "W" when blue buff are attacking you)
After blue buff, roll down to wolfs, use you W again, when it's out, finish them with another roll.
Now move into the middle of the wraiths, and attack the big one. after one basic attack, use your Q into them, and then turn W on, while still focusing the big one.
now move down to red buff, and keep hitting him with a Q/W combo.
Roll down to golems and take them with another Q/W combo.
here come the "tricky" part.
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At this picture here, the dark numbers are the jungle way, if the enemies dont have a jungler, the red are if they have one.
When you are done, you can normally start ganking, i will personally gank if i have half-full hp left.

When jungle are done, it's time to gank, and as always, Rammus always start the party.
Go into a bush, wait to you have a clear target to roll into, and avoid the enemey minions.
When your team are ready, start your Q, and wait till it's half done.
when it's half done, start ghost, and roll into a gank. when target are stunned, use E to taunt the target, and W for more damage. And let your teammates get the kills! only take the kill if noone else can get it.

If a lane need you to take over for some time, play defensive, stay safe, and hit when your teammates are ready for a gank.
Keep in mind that Rammus need a gank to kill/assist.

When a teamfight are about to start, roll into the support or the caryy. Use taunt on the one who deals the mosd AD damage, and then put W + ult on.