I make them out of a dozen 2x4s and a 3/4 solid core plywood, I rip the plywood 22" and 26" the top over hangs slightly and the frame is fit to the 22" for a under shelf all of it 8 foot long I cut off 3" off the 22" to fit under/in the center of of the legs & bottom frame. the top overhangs the frame and I screw it all together with glue on all the frame, (last two I made I didnt screw but used PL400 & framing nail gun. I have put up probably 8 or 10 of these and all of them are still holding up well. well the ones I still am around are doing well. I use them as storage shelves and work benches both. sounds of most of these benches they are made for storing semi engines to be rebuilt on them. anyhow have fun and dont over think it.
Mark