How much room they need very much depends on the quality of airflow and how often you want to change their litter out, and to some extent how large overall the enclosure is. I like using the really large mason tubs for rats, and 2 adult females per plus their litter seems to work pretty well for me. Adult males are being rotated through females, but if you have a smaller breeding operation, you will need a tub just for the couple of males when not with females breeding. Growout tubs isn't something you should need much of unless you are feeding a very large snake, as "weaned" rats are really not quite weaned and small is about the size they should be when leaving the moms and needing separated by sex at 6 weeks. If you are trying to feed something large like an adult boa, or retic or something like that, you could get away with 5-6 juvenile rats per tub so long as they don't have any young.
If you use smaller tubs like labs use, you will need a tub per female because of the room the babies take, and can probably only fit 2-3 juveniles per tub and they will need cleaned very often.