When the porch ceiling is super high, instead of buying outdoor fabric and then paying someone a small fortune to sew them, try this instead. Go to Lowes or your local hardware store, and buy big canvas drop-clothes in the paint section, and hang instead. This will cost you about $30. Will they mildew? Eventually, but so does outdoor fabric.
Of course you need a curtain rod and clips to hang them, and on this porch, Kruft Contracting, Inc. designed and hung a custom size curtain rod out of galvanized pipes (see pic 3 below).