Ours go inside to sleep and lay, but are always outside the rest of the time. If I wanted to improve the lot of our girls then, I'm pretty sure they'd prefer a run extension to a bigger house!
I'd agree with this absolutely. Since we're moving and penning the hens for the first time o protect the garden, I checked out the Soil Association standards. Basically, 6 birds / square metre for the house, 1 nest box / 6 hens, 18cm of aerial perch space per hen and 10 square metre of range.
They also recommend that the range should be rested for 9 months between batches - so effectively you need 30 square metres per hen, divided in to three areas, with the hens spending 20 weeks on each.
There are lots of other standards too but these are the main ones.
The house we have can accommodate, on this basis, 24 (floor area), 48 (perch length) and 42 (nestboxes). We're going for 40, based on the fact that they are rarely indoors.