Since you don't pay for wire by the square foot, how can you bid by the square foot?
A dwelling can cost $100/ft² with Formica countertop, pine & plywood cabinets, berber carpeting, force-air gas furnace and vinyl siding. You can build the same floor plan at 1,000/ft² with granite tops,solid cherry cabinets, Italian marble floors, geothermal heating and brick & stone exterior.
In order to provide an accurate price, you need to sit down with the homeowner(s) and have them make some decisions on what they want. If they can't think that far ahead, or won't, then your price (and by extension, your contract) needs to reflect that.
A dwelling can cost $100/ft² with Formica countertop, pine & plywood cabinets, berber carpeting, force-air gas furnace and vinyl siding. You can build the same floor plan at 1,000/ft² with granite tops,solid cherry cabinets, Italian marble floors, geothermal heating and brick & stone exterior.
In order to provide an accurate price, you need to sit down with the homeowner(s) and have them make some decisions on what they want. If they can't think that far ahead, or won't, then your price (and by extension, your contract) needs to reflect that.