My potting bench is a £5 plastic tray from Poundstretcher, which I stand on top of the small chest freezer in the shed. I do have one unit of proper aluminium staging in the greenhouse, but early in the year you need so much more. Until two weeks ago, I had the tiers from a small B & Q greenhouse (minus the cover) in the greenhouse. I went to move it, and all the plastic connectors disintegrated (exposure to sunlight I suspect). The metal bits are still OK, so I just need to improvise some supports.