[Image from John's Nautical & Boatbuilding Pages]
Buying a manufactured sail can be very expensive. If you are making your own vehicle and want to experiment with wind-driven propulsion, you might want to check out the idea of using building wrap as a way of forming your sails:
Now plan the sail. For this first sail, let’s not have battens; they would complicate things a lot. Draw a picture of it, and figure out if you can make the sail without a seam. Remember, as you draw it, there will be curve to the luff to shape the sail. And also, at each edge the sail will be two inches wider, for the taped hem. If you do need a seam, plan to use the edge of the material at the leach, and run the seam parallel to the leach, as in the sketch. Located in this way the force across the seam, tending to pull it apart, is kept at a minimum.
Let’s make the leach and foot absolutely straight, unless the foot is to be attached to a spar. But any edge attached to a spar needs to be curved in order to get shape into the sail. The deepest part of the curve, for a reasonably stiff mast, ought to be one third of the way up the luff from the tack, and its depth should be one inch for each five feet of luff (or foot). By the way, for now let’s call that point “D” for now. More about it later.
Now you need a gym or a dance floor, or something like that. You can guarantee the owner that you will not harm it. And you and your helper, if you have one, will for sure need a set of knee pads, like volleyball players and flooring people use, or you will come away with sore knees.
I like the suggestions on how to source the materials as inexpensively as possible, and the flexibility of the design. If you have tried this out, show us some photos or other documentation!
You can use the techniques for making a sail like this for your nascent parking lot surfer, kite, or other wind-powered transport. You will probably want to build and test a few before letting the shoreline leave your line of sight. Once you get the hang of the designing technique, then you may want to take the best of your plans to a professional sailmaker to have a formal, durable sail made up.