Mark and cut four pieces of 1-inch by 3-inch lumber to the desired dimensions of your prop size. You'll need two pieces of equal length and two sections of the same width. Line the pieces up to form a rectangle and attach them to each other with a nail gun. For large frames, such as those intended as scene backdrops, measure diagonally across the frame and cut two pieces of lumber to attach an "X" brace across the back of the frame.
Cut cardboard boxes open and lay them flat. Use small boxes for miniature props and large cartons, such as refrigerator boxes, for larger props or backdrops.
Measure and mark the dimensions used for your lumber frame onto the flattened box. Cut out the cardboard, lay it on the frame and attach it with a staple gun.
Cut muslin fabric to dimensions 6 inches longer and wider than the frame. Lay the fabric on the cardboard prop surface and smooth out any wrinkles. Wrap over the lumber frame to the backside along one edge and secure to the frame with a staple gun every 3 inches.
Pull each remaining edge taught and attach to the back of the frame with the staple gun. Cut away loose excess fabric near the staple line. Paint the desired prop on the muslin surface.