You could make it out of UHMWPE, the best current strength to weight material available. It's a plastic with density slightly under 1 kg/L. And it's UV resistant. Joining the parts is the real problem though. You could make it out of continuous thread in single piece with 3d knitting to avoid glue or fasteners. But all kinds of problems would arise. Also repairability would be bad. So probably you would use some sections and glue.