Determine the measurements of the greenhouse frame. Place one end of a tape measure at the top of the roof and extend the other end down toward the edge of the roof line to determine how long each plastic sheet should be. If the roof is rounded, follow the roof support braces to get an accurate measurement, then measure from the top of the greenhouse wall to the ground to determine how long each plastic wall sheet should be.
Lay the polycarbonate sheets or roll on a flat surface and use a tape measure and pencil to draw the cut line onto the plastic.
Install a hollow ground blade with 10 to 12 fine teeth per inch into a circular saw. A carbide-tipped saw blade is also acceptable.
Turn on the saw and cut through the polycarbonate plastic by following the pencil line that was previously drawn. Always wear eye protection and a mask when cutting the plastic to protect against injury from plastic particles and dust.