Finding the eight needed thin caps shown in the top photo is not easy.
TAP Plastic had something similar but only in red, which seemed very distracting. The actual original maker, CA Plugs of Buffalo NY, sells in bags of 200. More than I will likely ever need. So I stayed with normal 1″ PVC caps (bottom photo), as well as two standard 1/2″ caps for the horizontal crosspiece. The idea is to keep the four legs, especially the bottoms, from chipping and cracking. It is conjectured that sunlight will cause visible damage to the tops of the pipes, so the caps are really more pragmatic than professional looking. You may prefer to bevel the legs and ignore the caps on the top.
Besides the holes through the tops of the pipes of each leg – take care to measure the OUTSIDE diameter of the nominal 1/2″ horizontal crosspiece – you will need to drill 4 holes in each “sheet” and match them with the legs. Easiest is to clamp the sheets to the legs. Then either a bolt through the holes with a plastic washer on the outside (white works well) or paint a washer white and use a bolt cover. You will want some sort of plastic or lacquer coat on the sheets.