For most of my life I have been a renter and darkrooms have been pretty makeshift - any room that could be darkened, water and drain thru temporary hoses, and so forth.
In '97 I bought a 1920s vintage rural home, one built before indoor plumbing, and it has a strange floor plan. One bedroom (the only one on the main floor) opens into the living room and the bathroom (also the only one) is off that bedroom. So I made blackout shutters for the bedroom (semi-permanent) and the bathroom (removable) and light-proofed the bedroom door. As many of you know, there are certain advantages to a bathroom that's accessible in the dark! The picture is the present darkroom.
Since my basement tends to be very wet in the spring, it isn't useable for much else, so the intent is to move the darkroom down there. When I surveyed the basement for stray light, I realized it would be easier to light-proof the whole basement with a "tripple-90" entrance than to try to divide off part of the space. That should happen this year and will give me an 18x30 darkroom - OH THE LUXURY!