Stand on a ladder and hold a stud finder against the ceiling. Mark the location of the joists with a marker.
Measure the width and length of the ceiling using a tape measure. Measure the floor if it mimics the ceiling for faster results.
Determine how many drywall sheets you'll need by figuring the square footage. For instance, if the ceiling is 20-by-25 feet, you will need enough drywall sheets to cover 500 square feet. Drywall sheets are typically 4-by-8 feet, so you'll need at least 16 sheets of drywall.
Cut drywall panels to fit and completely cover the space, if necessary, using a drywall saw.
Hold the drywall sheets up against the ceiling and drive drywall screws into the joists with a screw gun to fasten the panel against the ceiling.
Adhere drywall tape to each joint where drywall panels meet, then spread joint compound over the tape with a putty knife, slightly overlapping the tape on either side. Let the joint compound dry for approximately four hours.
Put on goggles and a dust mask. Attach fine-grit sandpaper to a sander and sand over the joint compound, making it smooth and flush with the drywall panels.
Pour primer into a paint tray and use a roller to apply the primer to the drywall. Let the primer dry for three hours, then roll on the first coat of paint. After the first coat has dried about three to four hours later, roll on the second paint coat to finish.