The reasons why $/SF budgets seem ultimately unreliable as predictors of construction cost for a SPECIFIC new home building are confusing at best. Finished SF is the number you hear all the time from REALTORS and buyers. It's the number that includes all livable area, from outside wall to outside wall. But there is a second number you rarely hear about called Constructed SF which has a major impact on construction cost. It is Constructed SF that is one of the biggest factors in skewing $/SF rules of thumb. Just because the garage and basement and unfinished spaces are not livable, does not mean they are free to construct. Garages, unfinished and bonus spaces drive costs with no livable SF benefit. Hence the skew of Constructed vs. Finished SF. There is another key variable that makes the $/SF metric unreliable, and that is the quality of the amenitiesof the home's construction materials. Assume basic contractors interior finishes are priced, but what happens if there is a change to custom cherry kitchen cabinets, granite counters, hardwood & tile floors, whirlpool tubs, custom marble showers, etc? Did the Finished SF or Constructed SF increase? No. But the $/SF changed sustantially. This is why the you always get evasive price ranges and "It Depends" answers from contractors, architects and builders. In my opinion, this is why using $/SF for accurate home cost estimating will always be confusing to the consumer.

sure they can,

it all depends on their cost. a 2x4 cost the same in rural mississippi as it does in Los Angeles

No they cant. The building industry is loosing lots of builders daily. My area with holding values well has lost 20% of the new home builders with more in the wings to be lost.