Determine the length of the bulkhead ceiling and cut four 2-by-2 boards to that measurement with an electric miter saw. Think of these as the top and bottom boards of a wall. The vertical pieces that go between the top and bottom boards are studs.
Subtract 3inches from the height of the bulkhead. This is the length of the vertical pieces, or studs. Cut enough 2-by-2 boards this length to place one every 16 inches on the top and bottom boards.
Measure from one end of the top and bottom boards and make a mark every 16 inches. Drill a pilot hole on the marks with a 3/16-inch drill bit.
Secure the studs between the top and bottom boards through the pilot holes with the 2 1/2-inch drywall screws. These are the walls of the bulkhead. Lay them down and drill pilot holes through the top and bottom boards directly in line with the studs.
Deduct 3 inches from the depth of the bulkhead drop ceiling and cut as many 2-by-2 boards as you did for the studs. Secure them to the top and bottom boards with the drywall screws through the pilot holes. This is the box for the bulkhead drop down ceiling.