posted 10 years ago
I wouldn't say any county is better than other, just that they have different zoning regulations. For instance, if you were to do a search for "grays harbor county zoning" you would end up at their zoneing document:
http://www.co.grays-harbor.wa.us/info/pub_svcs/GHCCode/pdf/GHC17.pdf
In that document, you can find all the "permitted uses", "conditional uses" and "Prohibited uses". These will detail out what zoning will allow things like Accessory Dwelling Units, RV parks, Multi-family dwellings, etc. You'll see things like in the RURAL RESIDENTIAL DISTRICT section, you are allowed to have Mobile and RV parks in some circumstances, as well as one dwelling unit per acre.
It isn't necessarily easier if there is an existing house other than it is one less building you need to get permitted. And if you can convert an already existing building into a multifamily dwelling, that can simplify some things. But sometimes an existing house will be situated in such a way that you would not be able to create additional building lots (which is based on Building site verbiage in the zoning doc). It can be a blessing or a curse.
In general though, the more rural a county, the better availability of lots that have not already been carved up to the maximum extent. Those rural county planning departments are generally open to you calling them up and saying something like "I'm looking for a property where I can build two or three homes for me, my parents, and possibly my adult children, and wanted to know which zoning I should be looking at?" As long as you don't make it sound like you are trying to create some sort of militant survival retreat, they will be helpful. Then if you can find a property where you can build two or three homes, and find a similar property near by, you can get your 4 to 6 houses in a relatively close proximity.