first of all hi guys and i wish u can learn something from my guide to jungler rammus and sorry for Bad language ^^ .
Rammus always have to be tank for the team so Damage isn't your job.
Your job is how to tank and Grabbing enemy to your friends so for ppl who doesn't know how to play Rammus u need to hit q before engage and wait a bit for it to charge till u have enough speed to catch the enemy prefer to be in the nearest push to enemy and ping for ur friends that u going , when u go try to avoid minimoms (when they c u rollin' they always hide between minimoms !) hit him Taunt Him and press w ur friends will take care the rest .
Note: Flash is always good to across the minimoms if u having hard time to avoid them .
Note: sometimes ur friends r a bit far from u when u hit the enemy so try to Grab him after taunting its always work even with range cuz taunt isnt about u its always about The dmg from ur friends after taunting .
Note: if u didn't hit the enemy then drop it and search for another gank ,
but some times with high movement speed u can land a taunt even when u end up the q with out hitting someone.

First u go with Armor and 5 potions and start with blue after first clear u will have enough hp for clearing wraiths and wolves before u recall and u will have enough golds for Philosophers stone or u can have a gank if available which is always better choice.