Remove all hardware from the single-piece closet door with an appropriately sized screwdriver.
Measure and mark the pair of bi-fold hinged closet doors at 27 inches from the ground; cut them on the marks with a hand saw.
Space the two hinged closet doors 36 inches away from each other with the hinges facing inward and toward each other. Open each hinged door to a 45-degree angle, with the open angle facing outward from the space.
Center and place the single closet door on top of the two open, hinged doors. Mount a 3-inch L-bracket with the associated hardware and a screwdriver to each section of the hinged doors -- four in total -- to secure the single door as a desk top to complete the project.
Paint the finished desk in colors to complement your room.