Mine is brick, hommade brick built by my grandad in the 40s, with a cement floor. So far, it is slightly cooler when its hot, I think it will stay warm enough in the winter, ours are not too bad. Pics on my BYC webpage. Lots of work has been done since I last posted pics, and I have 7 week olds in there now.
As far as sturdy, I can't imagine anything getting into this fortress. I like the stone idea, it might be costly, but it could be beautiful too.
As far as sturdy, I can't imagine anything getting into this fortress. I like the stone idea, it might be costly, but it could be beautiful too.