I am starting a buissness and need to know how to bid a dry wall job? Is it by the sheet, or by the sq. and what is the average price

Let me get this straight you are starting a drywall company and you don't know how to bid the job? Hmmm. I own a drywall co and I bid jobs off blueprints I know exactly how many sheets of rock go into the job know how much mud, tape ,bead I need I know what the codes are in my area for fire stops. What area are you from prices vary from one area to another