Apply a strip of painter's tape in the corner where the ceiling meets the wall. Ask a friend to help you lift thin plastic sheeting up to the wall. Tape the plastic sheeting to the strip of painter's tape already on the wall.
Remove all the furniture from the room. Cover furniture with a dropcloth if it is impossible to remove it. Cover the entire floor with a dropcloth.
Remove the lid from a bucket of drywall mud. Stir the drywall mud with a mixing paddle powered by your drill. Add 1/2 cup water to the mud while mixing to make it thinner. Pour the drywall mud into a paint tray.
Dip a 3/4-inch nap painting roller into the mud. Start rolling in one of the room's corners. Roll down about 6 feet and stop. Start in the same corner but roll down the other side. Roll along the ceiling in an up-and-down pattern until a 6-by-6 foot square is rolled out. Roll over the square again, using a side-to-side pattern. Keep the mud about 1/8 inch thick.
Twist a slap brush onto a pole extension handle. Use the paint roller to apply drywall mud to the slap brush. Start on the two outside edges and gently slap the slap brush against the wet drywall mud to give it texture. Spin the brush 1/2 turn after every slap. Continue using the slap brush until the entire 6-by-6-foot square is textured.
Apply more drywall mud to another 6-by-6-foot section, using the 3/4-inch nap roller. Apply the mud in up-and-down and side-to-side patterns. Slap the wet mud with the slap brush to apply texture. Continue working in sections until the entire ceiling is textured. Allow the drywall mud to fully dry. Remove the plastic sheeting taped to the walls and roll up the painter's tarps.