Why I use Runic Echoes on Rammus
Rammus is recommended to build Cinderhulk- as most tanks are. But, I've found Runic Echoes to be far more effective for his kit.
A- Rammus' abilities scale off his Ability Power. Runic Echoes gives AP. B- Runic Echoes builds stacks with movement. Rammus Q (Powerball) enhances his movement. So Rammus can charge Runic Echoes with Powerball, and ram an enemy once it's filled for more POW. C- Runic Echoes procs of Rammus' W (Defensive Ball Curl). This means if Rammus has Thornmail, a maxed W, and Runic Echoes- the first person to hit him is in for some serious trouble. D- Rammus' Taunt doesn't deal damage, therefore the Runic Echoes won't proc until they hit his Defensive Ball Curl.
Basically, Cinderhullk is destructive to Rammus. Granted, he burns nearby enemies over time- but Rammus utilizes the Echoes damage much better. Rammus can come in with an Echoes charged, and punish the enemy team more quickly- before peeling off with his Q to charge Echoes some more, and come back for another explosive tank-session.
Rammus Jungle excels off 3 items.

Okay

. I personally think Runic Echoes is in a fine spot, it's just being abused by tanks because Cinderhulk is trash compared to the other options.