If you want to go cheap and cheerfull, pvc fabric from a general fabric and sewing shop is only £1a metre and if fitted on a hot day streaches nicely enough to give a reasonable fit. If you feel fussy you can stitch the front edges, and rear corners, it makes for a neater job then just folding. I found an ancient hand cranked Singer sewing machinewas up to the job of sewing this stuff in multiple layers. I also use it for sidecar roofs and so far the first atttemt roof is still ok after a decade of use, same for thd k3 seat I did over a decade ago, though it has been in a loft for most of that time so doesn't really count.
