T.'Bob,
You can do both, or either, just depends on what you're looking for. There's a whole lot more to making sails than is at first evident, it really isn't as simple as it 'looks'. But, if you aren't into racing, or getting the absolute mostest out of your boat, you don't have to have professionally made sails.
Almost any water proof, light weight, strong, 'not-very-stretchable' material will work. Even the blue 'Wal Mart' bags if you aren't too picky. Won't look too good on a museum quality three master, but I wouldn't put a custom suit of sails on a stick & board sail boat either.
There are a number of sailmakers for models, I can't give you a name or URL, but I'll bet there are plenty here who can.
Good luck and Merry Christmas...
- LtDoc