Drezella, that house/garage is amazing!
I got the plainest box I could from the shop, cut two archways in (one on long side and one on short side) to make a 'house'. To be be fair it looks more like a cave but it's gone down a treat, Biscuit is currently looking out of one 'door' and Fudge the other.
My attempt at making them a tunnel/run using old boxes didn't go as well. Biscuit flattened it and then Fudge went to the toilet on it (working together for a change!)