Seems interestingly legit...not gonna vote until I try it though, but I have a few suggestions:

1. Always have SOME Magic res. ALWAYS.
2. Try Madred's Bloodrazor. It gives Armor, AD, and AS. Your build is lacking AS, so I would recommend it.
3. Having both Warmog's Armor and Frozen Mallet seems kind of wasted imo, too much health isn't that good, but then again you're using atmas...
4. Cdr may be worth it, without your W you seem really weak and squishy.

Hey, I actually just played a game with rammus (he's free this week) and then came across your guide when looking how to to play him better. I ended up somewhat like your build (I improvised warmog's atmas after I got 3 gank kills early on) and thought my experiences might help.

Also, I was jungling. Never played rammus in lane, he's too weak imo.

I picked up Aegis of the Legion and Heart of Gold fairly early, and those helped me transition to mid-lategame tremendously. The Frozen Mallet isn't really necessary, I think. I would rather have a Force of Nature instead. At that point, I was already doing more with basics attacks than our pantheon :) Plus with slow from powerball and the taunt, I had all the cc i needed.

Overall, it was pretty fun to melt their soraka and veiger with one taunt. I would recommend building this way and I will definitely try it again :)

Thank you for the reply, I now updated the guide some and placed some BBCode in it. It is no longer as scary being a wall of text!

Thanks for the guides and feedback!

Hmm... a different take on Rammus... I like it! I'd suggest moving the point in Evasion to Vigor . Also Needs some BBCode. Right now it's just one huge wall of text.
Here is a great guide on BBCode:BBCode Guide.
And if you want to get fancy with it I'd recommend jhoijhoi's Guide To Making A Guide.

Thank you for the feedback, In the games where I used this there was only 1 or 2 AP carries so it wasn't that hard for me to ignore MR for the most part. I know it isn't the most viable build, but I have done surprisingly well with it and the only reason I got rid of my boots was because I was sitting on around 4-5k gold and wanted to try it out.

To do better I might replace the Atma's Impaler or thornmail with another phantom dancer instead and replace something else with a good MR or Health item. Thank you guys for the feedback.

I just had to write this build because it was great to be Rammus and able to zoom in and do 4-600 crits on thier guys. I was taking some of them down in Powerball/Taunt/W + 2 hits.

Oh, and the early thornmail was due to the people we were laneing against coupled with going for the extra damage in this build. This is very much a situational build if it is to be taken seriously.

*Update*
I posted a second build, and it might be more viable.

I'm not sure of your build.

For a start, thornmail is generally a last option item, even on Rammus and other taunters.

You may want boots if you don't rush double phantom dancers, as you move slow w/o your powerball.

Your magic resist is low, I'll only play this build if my opponents have little/no AP casters, which usually isn't the case. Relying on a single skill isn't gonna save me all the time.

In which case, you may want more HP in general, helping out your survivalbility and Atma combo.

Atma isn't a too good choice here. You get 11.25 damage from its armor, and from health, you get extra 54 damage, total of 65.25 attack damage.

With duo Phantoms/Boots of swiftness, you can easily chase down targets. With duo phantoms, you have 431 MS, more than enough to outrun targets. With Swiftness, you have 433 MS. But with a single phantom dancer, you end up with 371 MS, unable to chase with any target without powerball, thus having to resort to ganks or traps, even with Frozen Mallet.

Hope it helps :)

This is hilarious, I know what you meant by feeling kinda useless late-game, especialy in solo-que. I haven't tried this out with Rammus yet, but I did something similar with Malphite, and it was pretty tight. Bit trollish, but I can "roll" with that ;P