I ahve built several dollhouses over the years for others. Hobbly Lobby or Michael's is a good start and use the coupons , also check craiglist many people buy them and never complete them. I usually use a kit as a starting point then add or modify from there. Its basically just woodworking until you get to interior.
Another option , depending how large you want it to be is to look at model railroad structures. They are in wood or styrene and easy to modify.