Piece together sections of 1/2-inch particle board to equal the size of your box springs and mattress. For a twin size mattress, it is possible to use just one particle board cut to the correct dimensions. Lumber yards will custom-cut particle board at your request.
Assemble the base framework with 1-by-12-inch pine boards cut 2 inches smaller than the width and length of the platform. Use screws and wood glue to secure the pieces into a rectangular shape.
Screw L-brackets into the the platform and the base framework to attach them. Use 1-inch screws, and position the L-brackets two per corner on all corners sides of the base.
Add a 1-by-4-inch trim board along the entire perimeter of the platform to create a lip to keep the mattress and box spring secure. Drill pilot holes and use screws and wood glue to secure it to the platform. Countersink the screw heads and fill with wood putty.
Smooth the entire platform unit using 120-grit sandpaper. Stain or paint the unit as desired.