My momma hen is brooding outside in chilly Wales (no room in the hen house). I have provided her with a box, but she has chosen to roll the eggs out and sit outside, so I surrounded her with sheep hurdles and temporary fencing and placed a loose corrugated tin sheet over her head to protect her from rain. she is right by the side of the house, so predation is less of an issue.
Her last brood (just a few months ago) were hatched in a decaying rabbit hutch which she chose to brood her last clutch in. I covered the hutch with a similar arrangement as above and dragged it into a tumble down barn. (Can't do this now as the barn is being re-built).
Anyway, just to say that hens do seem to be able to brood successfully outside providing it is not really cold (and the chicks know to keep under momma if they are not warm enough). May not be ideal, but sometimes it is what you have to do because of lack of facilities.
A friend close by 'lost' one of her hens. No sign of the hen for a month.....she then reappeared a month later with 14 chicks in tow! It seems she had successfully brooded them near a main road with foxes, kites, crows and buzzards around and no human help. It had been a very wet and cold month with night time temperatures only in the 40's.
Aren't hens wonderful??
Sandie