New, unfired, cases are stored in their original container/package until I am ready to use them. They then get sized, prepped and loaded.
Used, once fire cases that i buy get resized, cleaned and prepped ready for use, then stored in ziploc bags and boxes. (I do not shoot where there is range brass to pick up.)
I have a certain amount of cases for each cartridges, several hundred or more for each different cartridge, that are in use. They get resized and cleaned shortly after shooting and are stored away until I decide I am short on inventory and need to reload them. As cases reach the end of their life, I replace them with stocks of new/purchased once fired cases.