Brian,
I made my own sails for around 20 years.
It's no big deal. Horizontal cut dacron sails are the easiest.
The radial cuts are usually designed and plotted with computer although this is not essential. They can be lofted by hand but there is more work involved.
When I first started I modified a domestic machine and drove it with two motors in series while I located an affordable industrial machine.

Once you get a good understanding of how the dynamics of the sail works it is a lot of fun. Designing, making and modifying and seeing the results.
This is just another aspect of what can be a really diverse
sport.
I must admit that I've finally given way to the pressures of time and no longer make my own sails. A good sailmaker can free up time to explore other aspects of the sport.

Regards,
Phill