I've been jungling rammus for notably over 2 years now. Most everyone's advice here is solid, but after pre-season 3 hit, I switched to madreds and AS marks (needing only 400 or so you can easily pick it up after a first rotation even if you stop to gank/get invaded) and then rush Boots of Mobility/Homeguard.
Not only is the speed intoxicating, but since you can literally make it from fountain to wolves in 8 seconds, it means from a practical sense that you can be at full life and mana all the time (thus skipping the practical for a spirit and philosophers stone.) At this point I usually work toward a Warmogs or Sunfire depending on my cash flow/confidence in my teams damage.
It was true before season 3, but now its more true. What you need on rammus isn't to dump truck armor, its health. His passive is a amazing, the reflect is amazing, but since your curl is a silly defense steroid, you can be absurdly tanky. After a notable engage, just recall, homeguard spin back and you're there in like, 10 seconds (plus your reaction time to ganks/middle turret attacks is great.)
I think focusing health on Rammus might be a bit harder since it makes the downtime on defense curl that much more punishing, but its very effective.