Building from scratch- Formula for dimensions

Hey guys, Im looking at building a purpose built home project studio, and was wondering what the general formula is for deciding the dimensions of the rooms to achieve decent acoustics and a flat response. I will have a CR, a live room, and possibly a vocal booth, and am looking to fit this all in to something approximately 25'x15'. Do you think this would be big enough, or are there good reasons for building bigger. The live room will predominantly be used for tracking drums, but I may want to use it for rehearsing with a band aswell. Im still in the preliminary stages at the moment, so I don't have a plan to show you. Are there any issues with partially building the studio under ground, other than damp proofing ofcourse? Cheers, snaregavel apologies if this is covered in another post.

Hello, Check out knightfly's 2nd response (about halfway done the page). http://johnlsayers.com/phpBB2/viewtopic.php?t=2472 and lots of good info here: http://www.saecollege.de/reference_material/index.html Hope this helps