Just itemize every aspect of the installation, giving every action a time frame.
Layout Boxes, drill, wire, make up, finish so on .. in a room of 4 outlets- 1 switch - 1 light box - 1 smoke detector, determine the time frame and material of the 7 items then divide by 7 say it comes out to 15 minutes and 10.00 material per location or opening, use that as your multiple throughout the entire floor plan, keep in mind the circuits will have a different time frame and material cost, then there's the panel .. its all about the time determined and materials anticipated once you develop a unit price per outlet - switch - circuit etc .. get out the calculator and start adding it up. Good luck.
