Most sails are computer cut, the sail maker tells the designer all the details, where the depth and shape is, lengths, curves, roach, type of boat. Then the designer designs it and cuts all the panles out, sail maker then puts it together.
If not computer cut a template is used for each panel for large amount of sails.
Skilled sailmakers can also floor cut one of or the first ones of sails, but that requiers and very good sailmaker.