Best Listening Room?


I am considering building an addition to my house, and figured I'd build a dedicated listening room while I am at it. So the question is, what is the best listening room one can reasonably build? Should it be square/rectangular or have tapered walls? Round corners? Should the ceiling/roof be high or low? Flat or angled? What is the best floor, wall and ceiling covering material? Etc etc... In other words: If you were to start from scratch, what would be the best room you could build?
njonker
see August Stereophile "Fine Tunes" P.154 by Jonathan Scull. George Cardas' ideas for reducing "slap echo" via asymmetrical wall dimensions; even tunable rooms with a tapered-angle sidewall on rollers (if you're actually building a room, might as well go all-out). Good article.
Positive Feedback is working on a series of articles about Winston Ma's listening room. I think somewhere around $300K was spent. It may share some ideas that can be utilized for much less. And, what is this stuff about walls on rollers? I hope that it is stable ...
Over at my dealers' he has these sort of CD rack looking things on the celing,right and left walls,No tube traps/or such. Sort of octagonal shapped wall behind the speakers./ no corners Any one been to Brooks Berdan's place?(So. Cal) Now to ans. the question Best room? mine/it's closer.Recres,the stable wall should be outside. Yes I'm keeping the day job.
I'm a building contractor. Of course the stable wall is on the outside. My concerns regard the ability of the "Wall on rollers" to not make noise or shake , rattle and roll during passages with extreme low frequencies. Ever hear one of those kids with 4 15 inch subwoofers in their car at the stoplight? That's where my concerns lie.