Bar spacing

[Sbramman]

I've got a spare metal grid from a rabbit cage i bought and i wondered if it would be suitable to use in building Freddie a setup. The bar spacing is 12mmx26mm (pic attatched) I've also found some thick plywood in the shed would this be suitable for the floor and the back panel? Also how would i treat the plywood to protect it from urine and chewing?
Thanks in advance
Sue