Cut plastic bag up both sides, across bottom and across the tops of the handles. You will need one half of the bag to make a pattern.
Draw 2 lines an inch apart at the bottom of your paper.
Line the bottom of the plastic bag up with the top line. You will need the inch below for seam allowance. Make marks at the top of the bag opening and the sides of the handles.
Remove the plastic bag and draw straight lines for the handles. Lay the pillowcase on top of your pattern, to make sure you make the pattern as wide as the pillowcase. Fold the paper in half. Draw curves at the bottom of the handles on both sides. Cut the pattern along those lines and unfold. I extended the length of the straps, but you can make them shorter if you like.