These benches have a low shelf under the main counter, and higher shallower shelf or two above the counter. Very easy to make with scrap wood. It is supposed to be crude and rustic. You only have to make it as deep as a book shelf, if you are just using it to hide the shed. Otherwise the counter is as deep as a kitchen counter, and the same heighth. The shelves below the countertop are as deep as you wish, and the shelves above the countertop are normal no deeper than bookshelves.

The countertop is usually boards laid across the frame with a gap between to allow water to drain through. You can stain it for a woodsy look, or paint it white, or green, and even crackle finish or use faux finishes. put garden items, or pots of flowers on shelves. Lean a wagon wheel against it. Decorate it up with pots of vines.

Painting a metal shed might not be bad, especially if it is already painted. For instance, a deep green with white potting benches in front, or a grey-taupe color, with dark wood stained benches in front for an English Tudor look.

I had to repaint aluminum storm window frames last summer because they had already been painted and the paint was flaking off. I just slabbed on white Painters Touch all purpose paint by Rustoleum from Sears. I like that paint. It is easy to use, cheap,grabs the metal and dries hard. It looks so much better than half painted and peeling. When you are painting something beat up and lousy what does it matter?