This paper covers research during which a large number of feral hives were dissected, described and analyzed. There is a whole lot of interesting information here. This information laid the ground work for Seeley's subsequent research on swarm behaviour. Decades later, this is still the source most people refer to for information regarding bees living on their own in tree cavities.
Some items of interest are cavity diameter and volume, comb width, as well as entrance position and size.