I recently started making my own strings and here's the resources I found most useful.
This tutorial is very clear:
Serving a bowstring:
This has a good layout to use if you want to make your own Flemish string jig (dirt cheap and easy):
http://poorfolkbows.com/flemish1.htm Making a serving tool:
Oh, it's worth mentioning that I reccomend 2 modifications to that flemish string jig as presented.
First, use a pair of heavier nails on the left side of the board as shown in that diagram. This makes a sturdy platform for twisting, as is used in that bearpaw video.
Second, put a nail every half an inch in order to be able to make bowstrings in 1" increments, instead of the 2" increments shown. To dial in the scale, just start with a single nail about midlength down the board to make your first bow string. Stretch it out as best as you can once you made it and see what length it comes out to. Place your length scale nails from there accordingly. Remember that shifting your scale a 1/4" will result in a 1/2" difference in your final strings. I would advise against writing a permanent set of numbers on the scale until you've made a few bowstrings to dial it in.