Determine the size of your theater flat. The size is determined by the artistic vision of the director and art department as well as what the material calls for in terms of scenery. For example, say you're building a flat that's 4 feet wide by 8 feet tall, which is a fairly standard flat size.
Cut two of the 1-inch by 4-inch by 8-foot lumber pieces in half using a saw. Use a tape measure and pencil to ensure accuracy. You'll use three of those pieces for the frame of the flat. Set the fourth aside for the brace.
Lay out the materials to form your drama flat frame. Each frame consists of two 1-inch by 4-inch by 8-foot lumber pieces on the sides and three 1-inch by 4-inch by 4-foot lumber pieces on the top, middle and bottom respectively. The middle beam is called the crossbeam.
Assemble the joints of your frame by using a drill with a screwdriver bit attached to insert two 3/4-inch screws at each place where two pieces of lumber join. This consists of the four corners and each side of the crossbeam located in the middle of the frame. The four corners and two sides of the crossbeam give a total of six locations where lumber joins to make the frame.
Use a saw to cut six triangles all with equal sides of 6 inches from plywood. Mark off the triangles using a ruler and pencil to ensure accuracy.
Place each triangle over the six joint locations on the frame. Two sides of the triangle will have wood underneath, while a third side won't in each case.
Attach the plywood triangles using your drill with a screwdriver bit attached and three 3/4-inch screws. The three corners of each plywood triangle will touch the wood frame. Insert a screw at each point.
Flip over the drama flat frame. The plywood triangle side will now be resting against the floor.
Lay the piece of plywood over the drama flat frame so that it's aligned on all sides.
Attach the plywood to the frame using 3/4-inch screws and your drill with a screwdriver bit. Place a screw about every three to four inches along the top, bottom and both sides of the frame.
Flip over the drama flat. The plywood will now rest against the floor.
Attach the fourth piece of 1-inch by 4-inch by 4-foot lumber that you set aside from Step 2 to the base of the frame using two 3/4-inch screws and your drill with the screwdriver bit. This piece will stick straight up into the air, be perpendicular to the flat and form a 90-degree angle where it's attached. Which side you attach the brace on the flat is up to you.
Attach a final piece of 1-inch by 4-inch by 8-foot piece of lumber to the outside of the frame and the outside of the brace that you just attached in Step 12, using four 3/4-inch screws and your drill with a screwdriver bit, with two screws in each respective location.
Stand the drama flat up so that it's resting on the brace.
Paint the drama flat as desired. Use large rollers or sprayers to cover big spaces in a short amount of time. Use smaller brushes for detail work. Make sure that you give each coat enough time to dry before adding the next layer of paint or detail work.