Following on from my previous post....
Here's the original inspiration - the Dell monitor packaging!
And the prototype (I cut in some external doors after I took this photo)
And in situ
Inky moved in there and started sleeping in there immediately
So I think we can say it's a hit. I'm going to look at a more permanent version as, while I haven't lifted it off since I bought it, I'm pretty sure that she will have gone a bit grand designs on it in places, where she has decided that an extra door would be beneficial.
I thought I'd come up with something new
but it turns out the Germans are already well ahead of us - Rodipet make something very similar
https://www.youtube.com/watch?v=IMB-N-UfMBI but they're quite pricey (about £32 inc. P&P) so I'll make my own to fit my cage