I'm thinking of making my own backpack style bag for my A1. Has anyone here done it and/or know any resources that I could refer to in the process?

Can't really help you but to say be careful what you pad it with. Most foam padding will off-gas and that apparently will eat at the coating on a lens. The foam you'll find in a quality camera bag or Pelican case will not do that. Where you would buy the right foam is a good question except you can buy refills for the foam that goes into a Pelican. Not cheap, I paid about a $100 for that a few years back.

Lowepro makes a good camera backpack complete with movable dividers and a rain cover.