Consider the use and placement of your trellis before you decide on the material you'd like it to be made from. Different materials age differently according to the wear and tear that occurs where they are place. This means exposure to elements and how often it will need to be cleaned. A trellis that is used for vines to climb up and around it may be cleaned less outside but the vines from the plants could cause their own wear and tear. A copper trellis may do well as indoor decor, where it won't have any exposure to the elements, but cleaning it could be a pain if it's placed somewhere up high or behind furniture. Consult a professional for the best results, and to get the most of your trellis product, whatever the use may be.