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The Pico cage really isn't very suitable, even as an add on, there's a real danger of falling with the height, possible bar climbing & poorly thought out levels & ladders, I wouldn't recommend it personally.
You'd really do better cutting your loses & starting over with one larger cage, they do better with one good size level & a nice deep base really.
Have you looked at the cages at Zooplus? There are some really good ones there.
The barney, alexander, alaska & hamster heaven are all good cages.