A two-level addition with our standard Beamed Exterior Wall System would add about 1500 sq. ft. to an antique colonial house in eastern Massachusetts. The lower level is about 1000 sq. ft. with a mudroom, bathroom/laundry, and office under a flat ceiling/Plaster and Beam Mid-Floor System, and a game room under a flat Plaster & Accent Beam Roof System. Upstairs is about 500 sq. ft. with a studio area under a cathedral Beamed Roof System with collar ties. Framing system specifications: https://www.postandbeam.com/package/specifications