Our hamster Red is kept in a Mill house from Rydon and she loves it! It is a fine size. Also, if the Gabber Rex would be too big for you there is another version called the Gabber Lux, which is slightly bigger than the millhouse from Rydon but smaller than a Gabber Rex. We keep our hamster Sonni in one of them, and it is fine for her. Here is a link to one on Ebay
http://cgi.ebay.co.uk/Gabber-Criceto-Lu ... dZViewItem
We find them, like the Gabber rex, great, though the holes at the going under the two platforms look quite small, so we cut them bigger.