This is a PDF pattern for a saddle bag purse. Recommended leather weight is 5 oz. 
 
In order to make this bag, you will need the following:
Enough leather for an exterior (5oz recommended if using a single layer, 2-3oz each if using exterior + lining, internal pocket (2-3 oz), and strap
2 dee rings
2 trigger snaps or similar
4 rivets
1 purse closure mechanism of your choice; I have marked the pattern with general placement for centering
Hardware + rivets for an adjustable strap, or leave it a fixed length