Cut plywood into three sections using a circular saw or eliminate this step by having the lumberyard do the job for you. You should have a 4-by-4 foot piece for the front of the stage and two side panels at 2-by-4 feet each. Sand the edges of the three panels to make them smooth and get rid of splinters that could potentially injure puppeteers.
Mark a section that will be used as the 14-by-36 inch stage window based on the heights of the children who will be using the puppet stage. Cut out the section using a jigsaw and sand this section well to remove rough edges.
Attach one side panel each to the front of each theater side by screwing four hinges and hinge plates to the inside walls at matching points. To ensure sidewall stability while in use, install two safety chains held by screw eyes at floor level so the sidewalls can't move more than 120 degrees.
Construct a removable shelf by cutting a 39-inch section of 1-by-6 inch wood. Sand and finish the edges. Make a shelf brace by cutting a 36-inch long section of the 1-by-2 inch pine. Center, glue and nail the smaller piece to the underside of the shelf. It should fit snuggly into the hole you created for the stage and rest against the front of the panel. Secure the shelf to the unit or keep it as a separate unit and put it into place only during performances.
Paint the theater front, side returns and shelf any color or combination of colors you choose. Make the façade of the traveling puppet theater as elaborate as you like. Consider a banner above the stage with the name of the theater scrolled along the top.
Install two brackets on the backside of the theater front to hold the curtain rod in place. Sew a stage curtain by cutting two 24-by-36 inch pieces of heavy fabric and hemming three sides of the curtain with a 5/8-inch hem. Make a sleeve for the curtain rod by creating a 2 1/2-inch pocket along the top of both panels. Feed the rod into both panels, snap the rod onto the brackets and fan out the curtain to hide the stage.
Rub the curtain rod with wax or oil to open and close stage curtains smoothly. Make the installation more professional by installing pulleys to open and close the curtains before and after performances.