This folding workbench consisted mostly of materials I already had on hand. It cost me less than $30 to make.
Step 1: Design constraints
The pictures below show where the bench will go. Before Christmas, this is where my desk was. Now my desk is directly below the camera, rotated the other way--there are perhaps four feet of space between it and the wall. (This was the primary motivation for making a folding bench; I still wanted room to push my chair back.)
My bench design began with a bit of serendipity. I found a discarded piece of 5/8" plywood in the lounge. It measured 24" by 48"--perfect!
Unfortunately, this piece of plywood was pretty ugly.