The go is to have the entry , garage and main living area plus master bedroom on one level if possible . It covers older people that way . A very important part of the market going forward .
Can you build them and just rent the second house out to cover the payments ? That way you get a new house and still benefit from the capital growth .
Tax benefits . Kicks the capital gain down the road and the depreciation on the renter is pretty handy in the first few years .