Start with the costs you can count. List material quantities and unit prices, estimate the hours for each phase, and add rentals, disposal, delivery, and other job-specific costs. Include setup and cleanup in your labor estimate.
Work through a simple example
Materials of $800, 20 hours of labor at $35, and $150 in other job costs add up to $1,650. At a $2,200 quote, projected gross job profit is $550 and gross margin is 25%. Track overhead separately and account for it when choosing your price.
Update the numbers when scope changes
Write down what is included. If a client asks for more work, record the price and schedule change before proceeding. After the job, compare actual costs with your estimate and use the difference to improve the next quote.
Use the Contractor Job Costing Calculator (https://payhip.com/b/xWZ9k) to run the numbers and the Estimate and Invoice Kit (https://payhip.com/b/FrCBI) to document the job.