For starters, you should know your material costs down pat. In my spreadsheet I have the exact prices I pay for 100 items. My assemblies are "real world" assemblies, but are parts only, no labor.
I bid a job by arriving at the exact cost for parts. Then I add labor. New houses aren't as plentiful these days as they used to be but when I was doing them every day, I was extremely confident bidding by the foot.
If you bid a 1500' house at $3 per foot, you will get the job and if you know how to work efficiently, you will do OK. However, there's something I call the "Large House Phenomenon", as houses get bigger, your square foot parts costs begin to drop. Around here if you bid a 3000' house at $3 per foot, you will be too high.
Obviously you add extra charges for sub panels, cans, low voltage.
My "standard" per foot price includes:
200 amp underground service
Wiring to code
Dishwasher and Disposal wiring
3 phones and 3 TV's
AC wiring within 20' of panel
4 interconnected smoke detectors.
10 recessed cans
Door bell and chime
3 ceiling fan boxes and fan assembly
I won't tell you what I charge per foot for this as I adjust for ceiling heights, etc, and pricing is a very local thing. But if my customer asks "how much will you charge me to wire a 2200' home?" I can without batting an eye give him a price and then enumerate all the items that price includes (see above).
After every job I thoroughly audit the job and see how I did, this provides the Feedback Loop you need to adjust your prices.
Sometimes I'm so busy I don't have the time to do a room by room takeoff, so I'll square foot it and tack on the extra goodies.
Square foot pricing does not mean pulling a number out of your butt, it means that if you know your costs and productivity expectations and you track and analyze everything, you can price jobs as accurately as assembly bidders.
Walk through your house right now, do a room by room takeoff. Add up all the assemblies and come up with what you would charge to wire your own house. Divide that price by your total square feet (I always include the garage, since I'll have to wire it) and the good news is you now have a baseline for square foot pricing.
The bad news is your price is too high! LOL.
