Hello and welcome to my Rammus build !

I made this build primarily for 5v5 in mind since there is some health / mana regen.
This build will give your team great benefits, and makes you a great support out on the field. With the cooldown reduction provided you can almost wear your Armordillo stance 24/7 and faster taunts can save or take lifes. Hope you enjoy ! Leave comment and vote if you feel like :)

About the build , try buy wards and put them up to avoid / make gangs. The last three chest + shield items are situational as i hope you understand ;) Take aegis if you dont feel like needing any of the other three chests more.
The item Core end with the Frozen heart.
The situational items starts after the Glacial Shroud , wards / aura item / or an epic chest depending on oponements :)

Although if there is not too much teamfights and you wanna milk the most out of your gp5s items you could start with one of the situational items, like Aegis of the legion.