Buy a house and rebuild it, or build a house?

I want my dream home, but I am unsure which option would be less expensive. Either buy a low priced home, knock it down then rebuild a house, or just buy land and build a house? I know if I buy land then build a house there will need to be a septic system and all of that put in. (My fiance is a carpenter, so labor costs would be lower than usual) Thanks for the help!