Set two 3/4-by-12-by-48-inch boards parallel to each other on the ground, on their long, thin edges. Have an assistant hold these boards, which are the side boards, in place and set a 3/4-by-12-by-40-inch board against one pair of ends. Position 1-inch metal L-brackets every 4 inches along the joints between the side boards and this board, which is the top board. Attach them in place with 3/4-inch wood screws. Repeat to add another 3/4-by-12-by-40-inch board on the other end of the side boards to be the bottom board.
Set a 3/4-by-40-by-49 1/2-inch plywood board on the ground. Put the assembled rectangular frame on top of it. Position metal L-brackets every 12 inches around the frame where it meets the large plywood board, which is the rear board. Attach the brackets with 3/4-inch wood screws.
Set a 3/4-by-12-by-38 1/2-inch board within the frame so that it is parallel to the top and bottom board, and it butts up against each side board directly in its center. Position L-brackets every 6 inches on the underside of this board, which is the middle board, against the side boards and rear board. Attach the brackets with 3/4-inch wood screws.
Put a 3/4-by-25 1/2-by-40-inch plywood board over the bottom half of the frame so that it covers the bottom board, the middle board and half of the side boards. Drill holes every 12 inches around the edge of this board, which is the front board, and into those boards underneath it. Attach the front board in place with 2-inch wood screws in these holes.
Position two 3/4-by-20-by-24-inch plywood boards over the top section of the frame to be the doors. Slide two side-mount cabinet hinges between each door and side board. Mark the locations of the screw holes, lifting the door boards if necessary and drill out the holes. Attach the hinges with 3/4-inch wood screws.
Position a three-part magnetic latch in the center of the top board and mark its screw holes on the top board and both doors. Drill out the holes and attach the latch with 3/4-inch wood screws.