Depending on the dimensions of the closet opening and the look you’re after, you can build a small closet door with plywood and other sheet goods, or even a prefab door panel cut to size. For prefab panels, consider louvered or frame-and-panel bifold doors (available in individual panels) that have a wide, solid-wood frame that you can trim without compromising the door’s structure or appearance. You can simplify any door project by making it an overlay design, in which the door mounts to the outer surface of the wall, eliminating the need for a door stop and the often tricky work of cutting a door to fit inside an opening.
Select the door material that best suits your needs and desired look. If you’ll be painting the door, use 3/4-inch paint-grade plywood or MDF (medium-density fiberboard); MDF is heavier than plywood but is exceptionally smooth and flat. For a wood-grain finish, consider 3/4-inch hardwood veneer plywood, available in a wide range of wood species. Once you’ve selected a door material, purchase two or three overlay-style hinges; these can include simple surface-mount hinges or Euro-style cabinet (“cup”) hinges that can mount to the inside of the closet opening.
Measure the closet opening and determine the dimensions of the door based on the desired amount of overlay (how much larger the door will be than the opening) and the installation requirements of the hinges (for instance, cabinet hinges may be limited to about 3/4 inch of overlay). Note: The bottom of the door should be kept at least 1/4 inch above the floor, for swing clearance.
Cut the door panel to the desired size, using a circular saw and a straightedge guide to ensure straight cuts. Round over the edges of the panel with a router and roundover bit, or simply sand the edges smooth with sandpaper, creating a slight roundover to prevent splintering. Finish the door as desired.
Fasten the hinges to the door, using the provided screws. Position the door over the opening, with its bottom edge set on 1/4-inch-thick spacers (made from any kind of scrap material), and mount the hinges to the wall or inside opening, as appropriate. Most closet openings should have 2 x 4 studs forming the sides of the opening frame; drive the hinge screws into a stud for strength.
Install a cabinet knob or pull onto the door at the desired height. Add self-adhesive felt or rubber bumpers on the inside face of the door, at the top and bottom corners opposite the hinge side, to protect the wall from contact with the door.