I'm looking at this thread after being away awhile. This is an aspect I was exploring myself. Especially since the game contains the Health/Sickness aspect. As a city's health deteriorates w population density, the logical benefit of building such buildings would be health. From this all other things come. Also, a city should not be able to grow beyond a certain point w/out certain buildings. Rome could not have been so large w/out multistory buildings, water/sanitation, and roads for rapid and stable transportation.
I would say a hut must provide health, as a caveman is much less likely to die of rain-driven pnemonia if he has a roof and walls. Things can be better secured, food better preserved against animals and weather-borne deterioration. With a stable center, any one or family or group can become more productive, by being more sheltered. Just the ability to hide behind something increases the battle benefit of a city. It won't stop bullets, but allows sneakiness.
You've introduced a magnificent way to enhance the game. These buildings shouldn't hold any negatives as I've seen so far. The game must be made to require such city enhancements. I can't fathom a building type costing more food... Just the presence of sheltering structures should increase food levels.
Default pan-unhealthiness should be higher, easy setting to change. Similar for unhappiness... The more people are sheltered and safe from perceivable threat, the less agitated they will be. Less likely to resist working, less likely to revolt.
I would say a hut would beat a hovel ANY day of the weak. A city should start w hovels as a free building once a certain tech level is reached. Otherwise, the city should read as containing a building, Unsheltered Open Terrain. And provide no benefits, just an understanding. Once you build the huts, the Unsheltered Open Terrain is replaced, and unbuildable. But returns if the buildings are razed.
Building-Dependant population caps is a system used in past games, but my be reflected using the health/sickness system. Buildings and techs that influence buildings increase a city's health, making it easier to grow. Want more than level 2? Huts... Want better health, attach the health percentage adjuster to Pottage/Aquaducts/Wells/Sewerage, etc... In addition to a raw health bonus to having such systems. Wells + 1 health. Aquaducts + 3 health. Pottage + 3 health. Every building also has a maintenance cost/factor. Take advantage of that. Bricks are better, but a house costs more to maintain than a hut...
As for naming all the different levels of housing. That seems fine for the description of a class of housing that you seek to build, but I wouldn't try to make all those types of housing individually buildable. Huts, Cottages, Houses, Apartments, Highrises, Skyscrapers, Archologies... And in the description of these 7 levels of housing one details the great varieties of wealth and poverty. The question here becomes, 'what technologies are required to make a building available?'.
The health effect of a housing building should be positive, as the housing is built singularly to support the needs of the people. The health problems come from the people crawling all over each other. The housing provides space for the people, to be apart from each other, to do their activities of daily living. Whole technologies are constantly being invented and forgotten that deal w these dilemmas.
And it's not just a building that does a body good, its the discipline and traditions of a people. The Japanese for example, unable to obtain the raw materials to build higher, learned to calm panics w ceremony, learned to live in tighter spaces by daily organization, learned to overcome stresses of confinement w communal excercise and ritual. These things must be an essential aspect of any civilization! The daily behavior and disciplines of a civilization define it, possibly moreso, than the technologies they discover, or the way they change their physical surroundings.
As for Health to Era... wouldn't be a function. Health benefit from functioning techs in a civ and the buildings/systems implemented.
+0h Bare Nature
+1h Huts
+2h Cottages
+3h Apartments
+4h Highrises
+5h Skyscrapers
+6h Archologies
These numbers are just rough. As we review the Sickness quotient of the per-population level, even at a 1 to 1 level, it quickly becomes apparent that technology becomes wildly influential on how we live.
Tech bonuses to buildings are available also, yes? Electricity can increase the productivity of buildings by +1 or better. The lightbulb for example. Refridgeration can increase the health of a building, by storing food better and keeping homes cooler in hot weather. Buildings can vary widely by the use of such a tag.
@Thunderbrd
You said "to assign pop to 'staff' housing would also explain some additional gold income as those people would still be out shopping and being taxed on that etc..."
I think this would be best done w specialists. They could be called Housekeepers, Groundskeepers, or possibly Servants. They would reduce gold, add production, add economy, and social stability.
Though I'm opposed to adding different 'classes' of housing as a building option in the cities, I think this feature would serve well. Servants.