Welcome to the forum.
I am not sure of any books per se, but know that for particular elements / products there are a number of YouTube videos on the subject. Weaver Leather does a great job on certain things, Don Gonzalez has great instructional videos on how to draw floral designs, Joe Meling has some great videos too. There are also several for how to create patterns for holsters, knife sheaths, etc.
What type of patterns and designs would you like to create??