With the bed box complete, place a level on the side rails and add shims underneath until the box is raised up just enough to be level.
Measure the distance between the floor and the bottom of the box. If the floor is carpeted, be sure to press the measuring tape to the floor surface for accuracy.
Use a table saw to rip MDF to the bed box width (55" in this example). Cut the front and bottom pieces according to measurements needed.
For the two end pieces, cut the profile of the footboard using a table saw for the long cuts and a jig saw to finish. Then, use the jig saw to cut out a notch for the trim at the top of the wall.
Assemble the pieces, starting with the board for the back of the box. Add a support block to hold the board to the box bottom. Apply glue, then brad-nail this support in place (Image 1).
Attach casters to the underside of the bottom board. At this point, only put screws in two of the holes (Image 2).
Attach the back board with the support block to the bottom. Use clamps to secure the two boards together, then pre-drill the remaining holes for the casters. Use 2-1/2" screws through the casters to draw the support block tight.
Add 1-1/4" wood screws to the assembly along the edge between the casters for additional strength.
Lay the front piece down and use bar clamps to hold all three pieces together. Add 2-1/2" screws through the caster holes and in-between to fasten the pieces securely.
At this point, a three-sided structure has been created. Place the end panels over the box end and fasten them with wood glue and brad nails.
Secure the panel with wood screws. Measure up 1-3/4" from the bottom of the end boards and use a countersink bit to pre-drill the holes.
Turn the unit around and repeat these steps (Image 3).
Cut four short and two long lengths of 1x2, sized to fit your installation, to frame the decorative end panel for the bed box.
Use a router or router table with a tongue-and-groove bit to rout a groove down the center of all frame pieces.
Use the same router bit to rout a decorative profile on the face of the frame pieces (Image 1).
Re-adjust the cutter blades and form a tongue on the ends of each of the short frame pieces. Cut them two at a time to keep the ends from tearing out.
After cutting, check the fit to be sure the frame pieces mate perfectly. Also check the assembled panel’s dimensions from corner to corner. If the measurements are equal, the assembly is square (Image 2).
When you dry-fit the frames, also measure for the plywood inserts that will go into each frame.
Cut 1/4" plywood to create three "faux" door panels for the decorative end panel. Size the plywood inserts 1/8” smaller in width and length than the dimensions of the frame grooves. This enables the plywood to “float” freely within the frames and allows for natural expansion.
Use glue to assemble the face frames. As you assemble them, insert the plywood sections but do not glue them in place. Check that the assembly is square and allow the glue to dry (Image 3).
Position the footboard under the bed box. Align the panel with the framing on the bookcases, using shims if needed. Tack the face frame to the footboard with brad nails, then remove this assembly and place it on its back.
Use 1-1/4" screws to permanently attach the face frame to the footboard.
Re-position the footboard below the bed box.
To complete the project, install trim at the top of the bed box to match the trim on the tops of the bookcases (Image 1).
Fill the countersunk screw holes with wood putty, as well as the nail holes on the trim pieces and door panels, and the seams along the sides of the bed box.
Lightly sand the footboard and the bed box (Image 2).
Vacuum away all dust, then prime and paint the footboard to match the bookcases (Image 3).
Paint the bed box to match the room’s walls (Image 4).
To hold the bed in an upright position when not in use, install ordinary sliding door bolts in the bookcases on both sides of the bed. Place the bolts underneath the shelves so they are completely out of sight. Mark holes for the bolts and drill through the bookcases into the bed box. Use screws to mount the bolts in place.