The fastest way to determine the cost of construction on a new home is to ask a local general contractor for the latest average cost per square foot of finish floor area. It won’t be accurate, but it is a good starting point. Two years ago, in my region, the answer was $150 per SF for a small, medium quality home, and an average of about $300 to $500 per SF for somewhat larger homes which tended to call for higher quaility as well. It has risen substantially since then, and it will be different in every region depending upon the availability of certain materials, how much shipping is required, the geological conditions on the land, the cost of living for the builders, and a variety of other factors. Also, one cannot calculate the cost of construction purely based upon the square footage of the floor area. That number is very easily shattered by a simple change such as complicated site preparation, fancy floors, or high end windows, or greater attention to insulation or heating techniques that require state of the art components.
Instead of relying upon square footage to tell me if I have exceeded your budget, I have to make regular overall assessments as I proceed with the planning. Then if you say “granite countertops” and “touch sensitive sink faucet fixtures” then I am going to look around for something else to slice off of the house to make that affordable. It’s a balancing act. If you are wealthy, this topic will seldom arise because luxury will trump cost in most cases. But most people have a limited budget. My obsession has always been to meet that budget the best I can. Then again, many people don’t build the house until 2 years after I design it. When that happens, some bets are off. There is never a better time to build a house than right now. Waiting always costs more. I don’t like to seem pessimistic, but I have never seen prices go down in the 30 years I have been in architecture. They slow down, but they don’t go down.