I used a solid/heavy flat wood door that my neighbor gave to me years ago. Kept the hinges on it and attached them to a wall in the laundry room, except sideways. Mounted two 2x4 legs to the underside front edge using another pair of hinges. Viola - a perfect bench that you can collapse the legs and the whole thing collapses against the wall (although that's never happened since the day I installed it...
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