30x18? Well, technically it can hold them. I use concrete tubs just a smidgin smaller for breeding animals.

What would I recommend? A multi level super pets cage. Go to pet warehouse, they have awesome prices, and sell extra levels and ramps for that cage too.

Check out craigslist too, I got a HUGE (really huge) cage for real cheap locally. $40 for something that originally costs like 150-200.