It is hard to tell you specifically what building costs are, since they vary so much, depending on style, siding, interior finishes, etc. Have you spoken with any builders? I would be happy to discuss options with you. there are so many bargains right now for existing homes, that new construction is going to have a hard time competing from a price perspective. 10 acres on Santa Rosa Sound is a huge amount of land --is this in Fort Walton Beach? Would love to talk to you about what you want to do.