I don't know if we've had a 'proper' thread about this yet, so I'll have a go:
Here's Oliver & Oscar's current base (they are free range, this just holds their food/ litter/ cozy area:
Here's another one of the same size when Oliver was free range and livin' on his own downstairs..many moons ago...
And here's just part of an old set-up I had. It was a 7 long x 2 (in some places 3) high x 2 deep
And I'm somewhat embarrassed to show this one now, but this was another oldie, before I knew better about proper size and such. They both had loads of run time (the room was theirs), but still, I feel bad that they were locked up in those at night
I would NEVER use a 3x2 anymore unless it was used as a base for free-rangers (as I'm doing now).