I made a nice little puppet theater from a cardboard box. It only required three cuts and some strong tape, no extra cardboard was necessary.
Materials: sturdy cardboard shipping box, utility knife, metal ruler, a pen or marker, strong tape such as clear duct tape.
Step 1: Sealing the back wall
Determine which side of your box is going to be the back wall of the theater; I used the side that had been the top of the shipping box.
First, tape down the flaps. Lay the long side flaps down first and tape them together at the seam in the middle. Then tape down the two shorter flaps, with a little bit of extra tape over the edges to keep them tight. I ordered them this way so that when you look inside the theater, the back wall is smooth and you could paint a backdrop right on the wall.
Step 2: Cutting the legs
Flip the box around so you are working on the bottom of the puppet theater. Using a nice strong ruler, cut through the box along both of the long sides about an inch and a quarter in from the edges. Then measure and find the middle of the box and make another cut through the box, perpendicular to the first two cuts. This makes two flaps which will be the legs of the theater.
Step 3: Opening up the stage front
Once you have the bottom of the theater opened up, open up the front of the theater. Push three of the flaps inside the theater: push one onto the ceiling and push the two side flaps onto the walls. Tape these three flaps to the inside of the theater. Take the fourth flap and fold it down outside the theater.