Measure the width and height of the bed and the depth of the cabinets.
Cut six legs for the base from 4-by-4 posts. From plywood or MDF, cut two rectangles the width of the bed and depth of the cabinets.
Lay one of the plywood rectangles on your work surface, and set the other aside. Attach a leg at each corner pointing upward, plus two legs at the center for extra support. Attach L brackets to two sides of each leg, with the longer part of the bracket along the legs and the shorter portion attached to the plywood.
Remove all hardware and sand the finish on the cabinets to prepare them for priming and painting. Wipe off any sawdust with a tack cloth.
Place one cabinet at each end of the base, and screw into place.
Place the second plywood rectangle on top of the mounted cabinets, and screw into place.
Cut another piece of plywood slightly larger than the opening left between the two cabinets and screw it into place from the back side.
Cut wooden trim to fit around the top edge of the cabinets and top shelf. Attach with finishing nails.
Fill the nail holes with wood filler. When dry, sand the surface smooth and wipe the surface with a tack cloth.
Prime the entire headboard, and apply at least two coats of paint. Once dried, rehang the cabinet doors.
In the area between the cabinets, use picture-hanging hardware to mount a large mirror or bulletin board.
Finish the cabinets with hardware that matches your bedroom decorating scheme.