That website above is similar to what I use, but I purchased the printed out plans from U braid it dot.com (take out the spaces).
It's a little different - takes a little longer to do. I've adjusted the knots to fit my ponies by bringing in a halter the size that fits the pony (s) I'm making the new halter for. I measure and put knots where the hardware is. If you don't want it too small, you need to add a little more space as the knots are smaller than the hardware and so will end up closer together, making the halter too small if you don't adjust it out a little bit.
The above website is the one that I started out ordering my book about braiding.
Braiding Tack That is where I got the general pattern for my headstalls, my lead ropes, collars and driving/lounge lines. I used the general ideas to come up with my own patterns for doing harness. If I really get busy with braiding, I could probably do a decent gig saddle, but I just use a purchased one - sooo much faster and since I saved $$ by making the rest of the harness - it's OK.
I've gotten my paracord from several different sources. Latest source is thru my farrier who also makes tack for sale. We went in together and I got 3 1,000 ft rolls of paracord (need a minimum of 5 rolls from this supplier at a time). The cost came to $120 for all that "string". My hubby got some for me from a supplier thru Amazon and just got 500 ft... Cost almost as much. The paracord from the above links also cost a bit more - but you don't get as much if you don't need it AND they sell by the foot if you'd prefer.
I've noticed both our tack stores and some catalogs are selling single strand paracord products that anyone can make!
Some of the other things that I made I made my own patterns (saddle pads) by using measurements of the saddles. Others I had patterns from magazines MANY years ago (Horseman, Horse Illustrated Year End English and Western mags).
Just about all my life, I've purchased rope and made lead ropes, lounge lines, trailer ties and cross ties in different styles. Still get rope from Lowe's, Home Depot and TSC. Some of the Natural Horse suppliers also will sell different sizes/types of rope (besides the ever popular Yacht rope) that can be made into your farm colors!