You can hire someone like John Sayers (http://www.johnlsayers.com) to do your studio design, then he'll provide detailed plans that you can give to a local contractor to handle the construction.
> does anyone know of a business that comes to your house and builds a recording studio ... in maryland <
Wes Lachot is excellent, and he's not too far away in North Carolina. Go to www.weslachot.com. His web site is still under contruction, but you can already see several of the fabulous studios he's built.