Saddle prototype

[Moorefieldc]

So I work in a machine shop and decided to make my own saddles instead of buying them. I have nothing to go off of besides pictures. I'm making two different kinds one to hold the panniers and one to hold a rifle securely. I need to know how big of a piece I need that sits on the pads that sit on the sides of the goats and that's really about it I can figure out the rest any input would be helpful.