Lay the two pieces that measure 30-by-24-inches flat on the floor next to each other. Measure up from one end and mark the center (should be 15-inches). Place the framing square on the line and draw a line across both pieces.
Stand one of the 30-by-24-inch pieces up on its edge. Run a bead of glue along the 24-inch edge of the 18-by-24-inch piece.
Place the glued edge against the line that you drew in Step 1 and secure the two pieces together with 8d finishing nails. Repeat this process for the other edge which will result in the three pieces forming the shape of an H. This is the centerpiece.
Lay the two 48-by-24-inch pieces on the floor next to each other. Mark the center of the 48-inch length and then make a mark 9-inches in both directions from that mark. Place the framing square on the mark and draw a line across both pieces. This will result in an 18-inch space between the two lines that you draw.
Run a bead of glue on the edges of the centerpiece and stand one of the 24-by-48-inch pieces on its edge. Secure it to the centerpiece with 8d finishing nails. Repeat this for the remaining 48-by-24-inch piece. Sand all exposed edges with 100 grit sandpaper.