Ive used melamine its strong as heck, heavier than you would ever imagine it to be and only "water resistant", it sooner or later gets through and rots apart especially if the monitor is strong enough to tear through the surface as Ive seen happen on one of Sobeks cages.
Ive used plexiglas, the less cleaning of it the better it scratches easy. If you use thin stuff it can crack or break when you least expect, but thicker stuff is very very strong.
Wood, or OSB has to be covered or coated to protect it from monitor claws, water, mold, etc.
For lining it, FRP is the best to line it with, strong, waterproof, etc.
Ive looked at 4x8 sheets of vinyl to line cages with for less than half what FRP costs but I dont think its as durable to weight, heat, claws, water, and time. Its also not as easy to work with because its flimsy.
Paint, sealant, etc etc, I dont like using it where they come in contact with it, they can tear it up, and its now useless. Paint, Ive used it out of their reach, but only indoor semigloss or satin latex or acrylic paint, that wont be in contact with anythinbg that will harm it, or on the outside, I stiil allow it to dry for 2 weeks minimum before putting the animal near it.