Lay out two 64-inch 2-by-4 boards with their long, thin sides facing downward. Position them so they're parallel with each other, 36 inches apart.
Slide two 36-inch 2-by-4 boards -- between and perpendicular to the longer boards -- with their long, thin surfaces facing down. Form a rectangular frame with the four boards that measures 39-by-64 inches. Drill two holes through the outside of each long board and into the end of each short board, for a total of eight holes. Attach the boards together with 2 1/2-inch wood screws.
Slide two more 36-inch 2-by-4 boards evenly spaced between the other 36-inch boards, with their long, wide surfaces touching the ground. Attach them in the same manner to complete the rear frame.
Repeat the previous steps to make a second identical front frame with two 64-inch boards and only two 36-inch boards, leaving out the internal pair of 2-by-4 boards.
Stand the two frames up, parallel to each other, on one of their 64-inch sides. Leave 17 inches of space between the frames. Position a 17-inch 2-by-4 between each set of corners on the two frames, so the 4-inch-wide surface of each 17-inch-long board is facing left and right.
Drill two holes through the front and rear frames and into the ends of each of the four 17-inch boards. Attach them in place with 5-inch wood screws.
Install four more 17-inch 2-by-4s between the front and rear frame boards along the long sides, even with the positions of the internal pair of 36-inch rear frame boards. Attach them in place using the same procedure as in Step 6.
Hold a 3/4-by-24-by-39-inch plywood board against each of the 24-by-39-inch sides of the cabinet. Attach the plywood to the cabinet frame with 1-inch wood screws spaced every 12 inches around the frame.
Rotate the cabinet to its rear surface and hold a 3/4-by-24-by-64-inch plywood board against its top and bottom surfaces. Attach each board in place with 1-inch wood screws spaced every 12 inches around the frame.
Set the cabinet on its front frame and lower a 3/4-by-39-by-65 1/2-inch plywood board down onto the rear frame. Attach it in place with 1-inch wood screws every 12 inches around the frame. Rotate the cabinet back on its rear surface.
Hold a 61-inch top sliding door track in place flush with the front of the top of the frame's opening. Attach it in place by drilling 1-inch wood screws through each attachment hole.
Position a 61-inch bottom sliding door track in place even with the front surface of the bottom of the frame's opening. Drive 1-inch wood screws through its attachment holes.
Set two 1/4-by-32-by-35 1/2-inch plywood door boards between the tracks by angling them up into the top track, then lowering them into the bottom track.