Usually exact size. All of the polycarbonate sheet we sell comes with a 10 yr warranty to not yellow or be effected by hail. Sheet must be installed with ribs running vertically on walls and with the slope on roof. Sheet size listed as sheet width x length. Order sufficient quantity, or a little extra.
Small shipments are costly.
For framing layout see Typical Layout for Multi-Wall Polycarbonate Over Wood Frame . Sheet thickness affects framing requirements. Also, -Fire Test Report if need. Dept. may request some of the above. Nov. 16 - Apr. 15 Orders Ship in 1 Week.