The Stitchback BP3 Mini Saddle Bag is a great beginner project. It does require knowledge of installing zippers, and utilizes small parts. This pattern to make your own bike bag is a great starting point for someone looking to create their own gear.
Foam stiffened bag
Bottom Velcro attachment straps
Overall dimensions: approx. 4"w X 5-1/4"d X 2-1/2"t