If you have to fit one to a curved wall, use poster board, or pressed cardboard etc. to make a pattern, You can take straight strips two inches wide and about six inches long, and just start on the side and tape them together one at a time to match the curve. Cut up a cereal box for the cheapest pattern material.
Fabric or Plastic? Your choice. I have used plastic - simply find a full size "tub" shower curtain you like, then cut down a curved side and install snaps. The trick to successfully sewing plastic is to place it between two layers of tissue paper so that the plastic won't stick to the plate or presser foot. You may want to lower or cover the feed dogs if your machine comes with a darning pressure plate or has adjustable feed dogs.