Wawte of time and resources I prefer them to make one home that will be upgradable that you can buy in any city and this stops from buying all other cities so they can focus to allow you to transform the home as you like , a city manor , a country villa , massive castle , a wizard's tower or even a Thievery hidespot... according to your gameplay style it would suit a lot better....
It seems to me like the argument of development time is against you in this argument because instead of making a dozen fairly generic houses that you can decorate you are asking for an in depth evolving manor that will be able to be made in many different ways. I feel like that is something that would take more work.
I personally would like a system where there is a house or two in each big city, and a few more rural houses on top of that but instead of being relatively easy to obtain I would like the cheapest to be in the range of 25,000 gold as t applies to Oblivion. The most expensive should be hundreds of thousands of gold pieces. You should however be able to rent rooms at inns for extended periods of time for 50-1000 gold depending on the quality of the inn.
A house that you could make would be nice as well and maybe it could follow the upgradable style that you were suggesting PROMETHEUS, but it should require you to purchase the land which would be fairly cheap depending on which of, maybe three-four plots of land you could buy. Then you should have to pay for people to help you build it and the more you pay them the shorter period of time it could take t build to your specifications.