What I would look for are Hollywood style theater or scenic flats. There are a lot of design drawings and how to videos out there and they are simple to build. For me, casters would not be neccessary as I would recomend using a french brace to hold the flats up right and or book or hinge them together so that they stand up like a storybook. They can be built out of 1 x 4 and covered with Luan or underlayment. Paneling will also work; although, it is not as strong as the luan. Check with your local lumber yards as sometimes they may have damaged or lower grade materials that will work for your purpose.
Here's a video from the Alabama Shakespeare Festival.
https://www.youtube.com/watch?v=NE4eIyGshD0Hope that helps
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Michael Johnson
Trinity High School
NC
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