Turn on the projector and cable tuner so that you'll know the size of your screen. Outline or mark the corners of the screen with a pencil; you will eventually have to paint over your marks.
Prep the wall behind your projector. Use a scraper to level and sand down any patches in the wall. Your image will project better if the projection plane is smooth. Place a drop cloth on the floor to catch any debris. Apply layers of wet joint compound where necessary; this will fill any holes in the wall. Allow 24 hours for drying, then use a heavy wooden sand block to eliminate any excess compound.
Connect the corner marks with the sweep of a pencil. Use the 8-foot length of rigid poplar stock as a straightedge. Place painter's tape outside of the screen area along the pencil lines. Use a cloth to rub down the tape. Seal the edge by pressing the putty knife over it. Put strips of blue masking tape on the outer edge so that the weight of the tape won't pull from the wall. Use your putty knife to apply a small amount of compound over the inner edge of the tape. Use fine-grit sandpaper to reveal the edge of masking after the compound dries. Use the wide-blade knife to put thin coats of compound on the screen area. Sand with fine-grit paper afterward and apply a coat of black alkyd-based paint over the wall. Allow the paint to dry, then sand down any bumps, fibers or imperfections in the paint.
Mix the black paint with a clean stirring stick. Use a high-quality foam roller to apply the first coat of black paint over the projection screen. Allow this base coat to dry, then apply a second layer of paint. This coat will take 24 hours to dry. After drying, use a fresh foam roller cover to apply a top coat of paint. Allow 48 hours for complete drying.
Put on latex gloves to avoid touching the powdery surface of the frame. Break the sealed edges along the masking area using the hobby knife. Lift away the masking so that you can see the hard screen edge. Cut the frame pieces from the preprimed baseboard stock. Measure the screen for width and height and translate the dimensions to the inner-edge measurements of the frame. Cut the frame members at the corners from a 45-degree angle. If necessary, sand all four frame pieces and apply two coats of black spray paint. After drying, mount the frame pieces and projector screen to the wall.