If you're a handy person around the house and have rolled in a piece of screen in the past, then you can do it. Zipper Flaps install just like a regular piece of screen.
It depends on the cage. You'll need to use a flat spline. Most always 310 spline is fine but some cages will require 315 splines.
If you feel like the spline is not holding well enough then 315 may be needed.
Home Depot, Lowes, Most any hardware store that carries screen will carry spline also.