In my jurisdiction the tax man is way ahead of you.

If the basement is roughed in for a bathroom whether the walls and fixtures are installed or not, its a bathroom and if you install a ceiling in the basement-its a finished basement.

To Lazy, it actually by definition is not finished and when they come to assess your property tell them that is not finished if you can not use it how can it be finished. For another conversation, If you remeasure your house from interior wall to interior wall you actually cut down your square footage and cut your cost of your house. Do you use the 6 inches of exterior walls?? You can't so they can not charge you for that space. They use outside dimensions because they are fast and easy. They also can not charge you for a vaulted ceiling in a foyer for the second story. They add this in your square footage but it is unusable space. Hope that Helps.