Have an assistant hold four 36-inch 2-by-4 boards upright and set a 1/2-by-18-by-18-inch plywood board on top of them. Arrange the four 2-by-4s, which are the legs of the stand, in the corners of the plywood board, so that largest exterior face of each leg is flush with one of the four sides of the plywood board, and the smallest exterior face of each leg is flush with the adjoining side. In this arrangement, each side of the plywood board will have a 2-inch side of 2-by-4 showing in one corner and a 4-inch side of 2-by-4 showing in the other corner.
Drill two holes down through the plywood board and into each of the legs using a wood drill bit that is slightly smaller in diameter than the wood screws. Screw 3-inch wood screws down through the plywood board, which is the support board, and into each leg to affix them together.
Set a 3/4-by-20-by-20-inch plywood board with its best surface facing down on the working surface. Place the support board and legs upside down on it and drill four holes with the same wood drill bit through the support board and into the larger board, which is the surface board, being careful not to drill through to the other side of surface board. Attach the boards together with 1-inch wood screws drilled into each hole.
Flip the stand back upright and set a 13-inch 2-by-4 board between each set of legs, on the inside, with its thinnest side facing upward. Drill two holes through each leg with the wood drill bit and into the ends of these smaller boards, which are the leg support boards. Attach the leg support boards to the legs with 3-inch wood screws.