My 2x9x4 cubes high cage was all zipties. Lots and lots and lots of zipties. Panels laid over panels for support. The bottom of the 2x9 was probably 3 panels thick in overlapping layers. My cages do not break.
If you can't use coroplast you can use ceramic or granite tile from the flooring section or something like plexiglass can be cut and then drilled to ziptie to the frame. Take a walk through one of the big hardware plus other things stores like menards or home depot. Our menards was a bit lacking but the home depot has a glass cutting area that also has a variety of plastics in various thicknesses. These can also be used around the edges and even sealed with a nontoxic silicone to the bottom piece if you want a shelf that contains poop and pee. It's a bit more involved and expensive than coro but chew proof and much longer lasting. I'm still reusing panels to other projects.
If you can't use coroplast you can use ceramic or granite tile from the flooring section or something like plexiglass can be cut and then drilled to ziptie to the frame. Take a walk through one of the big hardware plus other things stores like menards or home depot. Our menards was a bit lacking but the home depot has a glass cutting area that also has a variety of plastics in various thicknesses. These can also be used around the edges and even sealed with a nontoxic silicone to the bottom piece if you want a shelf that contains poop and pee. It's a bit more involved and expensive than coro but chew proof and much longer lasting. I'm still reusing panels to other projects.