
I could not keep mine in completely after 4 1/2 weeks old, LOL!!!
They stay in because they want to be with us, but if I would stay out with them they would be quite happy outside in all weathers, but then they are a hunting double coated Spitz.
Took two years before my first would use a bed of any sort, tiled floor was all she was happy with, though her descendants are quite happy with bedding in plastic beds, but often they kick it out.
I'd imagine that if you keep more than a handful of medium to large size dogs you will need to use kennels, just because you wouldn't be able to fit them all in the house at all times. It was certainly cheaper to get a double kennel built as their bedroom, than an extension.