Rammus is extremely strong with the buff to Iceborn Gauntlet and changes to Last Whisper (also, it seems like nobody builds LW at all no matter how much armor you get these days).
Runes: Flat armor marks, scaling armor seals, scaling magic resist glyphs, one movespeed quint, and two scaling cooldown reduction quints.
https://gyazo.com/39db1f13569512bc91e7cff7aabf83cd
Rammus benefits a lot from CDR but has a hard time itemizing it. I like to take armor marks because armor is Rammus's primary offensive stat anyway, but you can run attack speed instead if you want.
Masteries: 12/0/18 with Bond of Stone for your keystone.
https://gyazo.com/861e52fc3763a0689a2c8ab7381d7961
Next patch, Strength of the Ages is getting buffed really hard. Since Rammus has very bad base and per level health stats, take Strength of the Ages as your keystone from that point on.
Summoner's Spells:
or
Rammus has outrageous synergy with TP + Homeguards and is not in need of an escape.
Skill Order: W, Q, W, E, max R, max W, max Q, max E.
Easily the point of highest contention. Most people max E over Q. Some people max Q over W. Some people put two points in W then leave it to max last. You're probably gonna have to experiment and see what fits you best, but the highest winrate order is W, Q, W, E, max R, max E, max W, max Q.
Item Build:
Be sure to start hunter's talisman and three health potions. Feel free to swap in merc treads or mobis based off of who's fed on the enemy team or when and how much you want to gank. Deadman's and Iceborn are absolutely core, giving you everything you need to catch and stick to your targets. Note that your Iceborn proc scales with armor, and will create a noticeably bigger slowing field if your W is turned on. Banshee's is listed as the desired magic resist item, but all of these options are still fantastic for Rammus:
. Stay away from Warden's Mail items since they will also reduce your own damage output (fewer procs of your W).