Determine the coverage area for each color and estimate the number of gallons you'll need for each. For odd walls with angled ceilings, make your best guess. If you're not comfortable doing this, measure the wall at its highest height and multiply that by its width. Now subtract the lowest height from the highest height, multiply that number by the width, cut that answer in half, and finally subtract that new number from the original height by width. That should give you the wall area.
Do the cleanup. When the painting is done, send the painter home and do the cleanup work yourself. This will include rolling up drop cloths and collecting scrapings, removing painter's tape (use a hair dryer on low heat to soften the adhesive), cleaning paint brushes, rollers, and other tools, replacing electric switch plates, outlet covers, and light fixtures, and sealing any leftover paint cans and storing them in a dry, temperature-controlled location.
Painting a brand new house with smooth surfaces dramatically reduces prep work. On the other hand, if you’re painting an old home with peeling walls or siding, it’s going to take a lot longer. When deciding whether to hire house painting professionals or do it yourself, take the current state of the paint into consideration. If you’re not up for the challenge of scraping and sanding for hours, you should hire help to get the best results.
Most of a projects price is the cost of labor at $25 to $75 per hour. However, most contractors bid out based on the entire project which includes all work hours. Hourly rates are only useful if your pro asks to do the job as “time and materials.” However, be wary of this pricing structure, it usually shows the contractor is uncertain how long the project will take.