Here's my garden stool project so far. The ends and top are a 3/4 inch thick wooden plank, 11" wide. The back and bottom are from a piece of 3/4 " thick plywood. The supporting parts are cut from 2 x 2's. All of this was from the wood storage shed.
I based the height on a metal garden stool that is about right but becoming bent and wonky. I decided I want it about 3 inches taller, to suit my legs. Since it will be heavier than the old stool, it will be on casters. I chose 6" casters, which add 7" height. So, I subtracted that. That's good, because more weight means heavier stool.
Here are the cut parts just sitting there. View of the front, which will be open to hold tools and stuff.
Back view. Back is closed, to give rigidity.
I've assembled most of the top, using deck screws. I think I'll back them back out, and apply liquid nails before re-screwing it together. That should give more strength and rigidity.
Using 2x2s as shown on the bottom, will give strength for the casters. I might use a hole saw to cut openings in the ends, to lighten the weight a little. The back too, if a practice piece of plywood cuts OK. I ordered a pad for the seat. It will need a pull handle or rope. Once the wooden parts are assembled, I will apply a coat of deck stain, same as the raised beds have.