price per sq ft is difficult to nail because everyone has a different trim level to which they are completing the home. Some people include fees and others do not. Some include the garage, some do not, some even include it in the price per sq ft calculation.
I would argue that price per sq ft is based on the home sq ft and therefore the garage is thrown into the numbers.
Also what trim level are you at? 1/2" drywall with plastic fixtures, particle board vanities and cabinets, and fha minimum grade throughout or 3/4" drywall, 10' ceilings, granite, wood tongue & groove cabinets, deep sinks, 9" faucets, smooth stucco, and full interior trim?
What is it that you are doing.
With all of that said, a basic 1300 sq ft home with 22x22 sq ft garage with FHA minimum trim level, comp roof, single gable, fake pergo, wood cabinets, granite - $50 sq ft, in CA, based on the sq ft for the home.
Of course fees here, water meter, sewer, etc will be another $40K.