I've thought about a diy room similar in scope, but with the addition of a slight angle from about 3' high down to the floor to minimize bass magnification at the wall/floor corner. Of course mine is a non-scientific approach eliminating deep corners were bass is magnified.

On a personal note, I don't care for solo rooms with only one chair. They seem solitary and lonely. I'd have 2 or 3 chairs to accommodate visitors and friends. Just my 2¢