Profit must be calculated as a percentage not of cost, but of the final selling price.

We concluded the last article with a sample problem, as follows: You have taken on a job for which your total cost is $1,000. You wish to make 10 percent profit on the job. How much do you have to charge the customer in order to make your profit goal? Probably nine out of 10 roofing contractors are inclined to figure it at $1,100. Wrong.