Draw a rectangle in the center of the box lid. Cut the rectangle out with a utility knife; this opens a space for the glass pane. The edges of the box are your shadow box frame.
Smooth rough edges with fine-grit sandpaper.
Cover the frame with decorative paper. This can be wallpaper, wrapping paper or something more creative, such as an old map. Cut the paper to the size of the frame plus an additional half-inch on all sides. If you box lid frame is 12 inches wide and 12 inches long, cut the paper 13-inches wide and 13-inches long.
Place the paper, right side down, on a table. Use spray on adhesive glue to coat the top and sides of the lid. Center the lid onto the paper. Cut out the middle rectangle of the paper with a utility knife, again to open it up for the glass pane.
Cut a small square in the paper at each corner. This creates a fold for the corners. Starting on the bottom edge at the right corner, cut the paper flap, towards the box, until you reach the edge of the lid, then turn the lid and repeat that step on the next side. With each corner, you remove a small square of paper, leaving a void in the flaps.
Fold the sides up and over the edges of the frame, smoothing the paper down as you go. Reapply glue if necessary to make it stick. Let the glue dry.
Paint the inside of the frame with contact cement. Place the glass pane inside the frame on top of the contact cement. Set the frame aside to allow the cement to dry. Put a heavy book on top of the glass to help secure it while drying.
Spray the bottom of the box with adhesive, and then line it with colored paper. When the glass and frame have dried, fit the two pieces together to form the shadow box.