If you are interested in an alternative to traditional cages, you can check out C&C (metal grid) cages in our housing section and have a look at what you can do with them. They are cheap and far more flexible and adaptable to your special requirements; and can easily extended to a two storey cage. Grids and correx for the cage trays are widely available. I am sure that our bargain specialists can give you the best durrent deals!
Traditional cages may be a better option if you have other pets like dogs or cats.