Built them from wire we bought from Klubertanz. More expensive but heavier than the kind you can get at the stores. Noticeably sturdier and don't rust nearly as fast.
I have wooden nest boxes with fine gauge wire mesh bottoms that I put in as needed. All wood that comes in direct contact with urine is coated with epoxy resin, super easy to keep clean.
I really like the pull-out trays. Easy to scrape and hose out. Get an extra to swap in when you're cleaning, it's like they wait for you to pull it out to make a big mess.
I have the plastic resting mats so they can get off the wire if it's bothering them.