We had a NORBO Ikea folding table laying around, and I liked the idea of having a workspace when I needed it, and open space when I didn't. I installed it, but, as you recall, the studs aren't at 16". So I attached a 2x4 the width of the table to the existing studs, and another one down a stud, and attached the table to that. I put leftover 1x3s in the space between the table and the wall to remove the gap.
We primed and painted some leftover plywood (from the floor) and made two shelves out of it along the siding side of the greenhouse. We didn't want to block any sun with our shelves, but wanted space to put wider plants.
Way on top are some shelves made of leftover closet material. I attached it using scraps of 1x3. I wanted shelving that wouldn't block the light.
Between the studs on the light sides of the greenhouse are pieces of plywood and scrap 1x4s and 1x3s cut to the width of the studs as shelves. They are at different heights so we could screw them in from the opposite side of the stud and for visual variety. We also wanted as much space as possible in which to walk and wanted to minimize light blockage.
Here is a finished exterior photo, with the coop so you can see how far away the coop and greenhouse are.