If you are building a large headboard, you will have to do so in the bedroom itself, and that may well require that you take the bed out of the room to provide enough floor space. You should cover the floor with a protective tarp. Cut the plywood pieces for the panel to size and set them flat on the floor. Attach a couple of 1-by-4 boards to support the panel, and then flip it over. Cut the batting long enough to lap around the edges of the plywood a few inches. Set the batting aside and spray some adhesive or spread some glue on the plywood. Quickly, and carefully, set the batting in place and let the adhesive dry.

Set the fabric on top of the batting. Ideally, you will be able to use only a single piece of fabric. If you need to join two pieces of fabric, plan to locate the stitched section beneath one of the grid boards. Allow about 6 inches of fabric to overlap on all sides. Pull the fabric around the edge of the plywood and attach it with a staple gun on the backside. Take care to form neat, tight corners. Note that you do not necessarily need to attach batting and fabric to the panel below the mattress line, as long as you are certain that the bottom portion will be thoroughly concealed by the bed.

Build the Frame

Set the panel against the wall and build the frame on the floor. Cut four boards long enough for the panel to fit snugly. Attach the boards with screws or nails at the corners, making sure that the corners are perfectly square.

Build the Grid

Use a strong hardwood for the grids. I would probably choose oak or maple, cut into 1 and a 1/2-inch squares. Since you want to keep both the inside and outside faces of the grid on the same plane, you will need to join the separate pieces with half-lap joints. For grid strips measuring exactly 1 and a 1/2-inches square, you would need to cut laps exactly 3/4-inch deep by 1 and a 1/2-inches wide at each joint. You would then form the grid at the laps. Cutting the laps can be quite simple with a table saw equipped with a dado blade or a bench-mounted router, and a bit more involved with other tools. You will need to cut to the proper depth with a power or hand saw, then use a chisel to finish the cut. After cutting all of the laps, assemble the pieces to make sure that all of the joints fit perfectly, are properly aligned, and fit snugly inside the frame. When you are satisfied with the results, assemble the grid using glue and short screws or nails driven through the back (where they won't be visible).