The Roost is a little hole in the wall. You will get a bed in a tiny room. It's not very nice but it's perfect if you just need a place to crash at night and are skiing Vail or Beaver Creek all day so you won't really spend any time in your room. Hotel Frisco is definately nicer than the Roost. The altitude difference is not that significant so if you are having issues in Frisco, you will probably still have them in Vail. Also, what you save by staying in the Roost will quickly disappear to the higher prices of food, gas, etc. in Vail. The only reason to stay at the Roost would be if you are skiing Vail or Beaver Creek everyday and want to be closer (but Frisco is much closer to Keystone, Breck, Copper, A-Basin, and Loveland). If altitude is the issue, stick with Frisco.
"The world would be a better place if everyone kayaked."-Brad Ludden (Valhalla)
"You only get one chance to run a drop blind."-DD