The best model for home-made panniers are probably carradice , which are basically home-made in the factory.
The material is heavy duty canvas which is very tough and water resistant.
Backing and base stiffening material is corrugated plastic (For-Sale sign) fixed by rivets. This forms the internal surface, there is no lining.
The shape of the bag is designed with a heel cutout, the front edge is angled inwards towards the base so you can mount them further forward on the rack.
The mounts are Rixen and Kaul Klick-Fix which slide onto rails rivetted onto the material and stiffener.
There are no zippers, one rear external pocket, a generous nylon extendable collar with cinch closure and a large flap-top with Fastex back-pack type buckles.

Klickfix is used by a number of pannier companies, it is a quick-release, locking system which is tried and tested and will not bounce off and