I used this:
3x Attack Speed quints
9x Attack Speed marks
9x Flat armor seals
9x Scaling MR glyphs
For masteries I took:
5/22/3
Cooldown and Expose Weakness in Offense (because you aren't playing rammus for damage)
Any tank stats you want in Defense (varied)
Movespeed in utility (because rammus is all about going fast and I didn't want to put more points in defense or offense)
This probably isn't optimal but is what I took
I take the attack speed to clear the jungle faster (cuz god, your clears are slow) and the armor and MR for overall tankiness (cuz you aren't playing rammus for the damage that's for sure.
For items you should always build
There is no other option. The new jungle will kill you and you won't be able to clear at all without this. Then, just build full tank.
I haven't played him in 4.20 (I think he's weaker now) but I figure its probably the same about.