Here are some pics of a maternity rack that I made about 2-3 years ago. Each tub will hold three or 4 adult rats, I usually have 1-2 females with litters in each tub, but I've had small breeding groups in them before and they work fine as long as I move the prego moms out.

Front


Side


Back


These use Jumbo cat litter pans as tubs and I've never had a rat chew their way out of these.

Mark