Begin by cutting out the pieces (including lining pieces if you require a lining). Mark the ZIP END on the FRONT of the chaps.
If you are using a waterproof fabric, you will want to avoid using pins that will leave a permanent mark on the fabric. Use clips or pegs instead.
To make applying the bias binding easier, lay the outer pieces WRONG SIDES together with the lining. Use the clips to hold the outer fabric together with the lining while you stitch. Stitch a 5mm row all around the seam allowances in order as shown. The lining fabrics may stretch as you sew, after each row adjust and trim to meet the outer fabric.