You can buy or make pans for Critter Nations. Most people use fleece on the levels and pelleted paper in the litter box but some people do have pans. Check out the CN pictures thread in the Habitat section to get an idea.
The cage you're thinking of (purple base, green tunnels) is big enough but it doesn't use space very well, it's a good idea to add some levels yourself. More so, it's unsteady so if you have other animals, the top can easily be knocked off the base and the rats would be at risk. If there are no cats and dogs in the home, that woulnd't be an issue.The plastic shelves on those cages also smell awful when they come into contact with rat pee so you'll have to clean them often.
The cage is big enough, it's just not my favourite.