I have made some hair buckels. I have very long and thick hair, so I find it hard to find pretty hair accessories in stores.
I have made them both with bracelet patterns and with free form beading or my own pre-planned patterns.
When using a bracelet pattern, make sure it is wide enough. It is easier to use a piece of cardboard to stiffen the beadwork if it is to wide than using a too narrow strip to cover the buckle. If the pattern you want to use is to narrow you basically have two choices: make it wider or use bigger beads.
The biggest challenge, however, is sewing the beadwork onto the buckle in a good-looking way. For this I can not give you any advice. You have to go with the flow when doing it. Sew it on in a way that seems suitable there and then. I have never done two beckles in the same way!