It pains me to read on here how fast everyone thinks they are. You might be, and you might beat me on speed, but I play a different game, I bill for skill and quality. Guess what? When you do quality work and not play, "who can do it fastest," you'll be happier, work more safely, and make more profit for less effort.
To the OP, square foot pricing is good for one thing, and one thing only; it should be an internal number that you use to measure the results of one project against similar projects. The thing that no one tells you with The square foot race to the bottom method of bidding work is that there is a SF price for the rough, a SF price for the trim, and a SF price for the service, and a price list for extra's. GC's think they love having subs compete using SF figures, but what they don't know, or don't get, is they are only comparing dollar amounts, and not what will actually end up inside the box they are building. How about this instead, you are going to get x 15 amp TR duplex receptacles with white nylon cover plates in bedroom 1, xx 15 amp TR duplex receptacles in the dining room on a 20 amp 120 volt circuit. A 200 amp 40 ckt. Square D panel. and all of this (rough service, trim) is going to cost you $XX,XXX. Now Mr. GC you can see exactly what I'm including and exactly what it will cost you. And, oh yeah, the payments will be 30% to start the rough, 40% Upon the completion of the rough, and the remaining balance upon completion. (make up your own draw percentages) Besides, who measures the square footage, is it the inside of the walls, the foot print, do basements count? Fabric, my friends is sold by the square foot (yard actually) houses are sold by what they are made of, what is inside of them, and where they are. Get it? I'm in an off mood tonight, can you tell?
And if at all possible, work direct for the homeowner, who really needs a GC?