blueline leather

Hello all, I have recently decided to attempt building a saddle, I'm sure there will be many more questions in the future however the one thats stumping me currently is a pattern for my swell cover, i purchased the encyclopedias from tandy's and watched the JWP videos, but i am building a mod assotiation and the patterns I have will not work, should i use chap leather and experiment or what? any suggestions will be very helpful Thank you Cody