Thanks everyone!

I'm glad you like it.
Do you mean that you want the ramp to go to the top of the pet store cage and then another ramp to go down into it? I think those ramps will be far too steep.
I've gotten a wooden organizer from Micheal's that hollow inside (so I can carve out a hidey) and has a solid diagonal side. I put in the cage and it didn't seem too steep. I let i stretch the hole width of the cage except for a space big enough for them to get off the ramp.
Edit: The metal cage bars on that side will be gone. The ramp will only have to cover about 6" worth of plastic bottom.
I've also seen Blondie scamper up steeper slopes, (like my book-bag, for example) much to my horror. :melodrama
Using your pet store cage as a second level will work just fine, but I would cut out part of a side of it so the ramp can go directly from the main level to the store cage. Check out the galleries--there are lots of good ideas there.
I'll probably end up doing that; I was just hoping not to have to so I could take the cage apart if I need to, or just wanted to change it. I know i'll be upgrading it all the time.
Thanks for the help!
Is there anything thing else I can build with wood other than hideys for them? There's a sale going on for 2x4s in the Warehouse in my town. I want to know if I should stock up now.