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.