All good comments above. The one point I'd add is to think about building the room with ASC "Wall-Damp IsoWall" panels, or something comparable. See the following link to ASC's web site for more info about "Wall-Damp IsoWall":
http://www.asc-hifi.com/products/isowall.htm
Having the correct dimensions for your listening room, with proper speaker placement, etc., is certainly vital, but if you are going to build a dedicated room, do it right and be sure your walls are acoustically dampened.
http://www.asc-hifi.com/products/isowall.htm
Having the correct dimensions for your listening room, with proper speaker placement, etc., is certainly vital, but if you are going to build a dedicated room, do it right and be sure your walls are acoustically dampened.