So I decided to go with the paid addon Archipack rather than the free version or ArchiMesh which comes with Blender by default. Archimesh was giving me too many strange behaviours, although I’m not sure that ArchiPack won’t do that too on better acquaintance.
Anyway, I whipped up a cottage with a single room, door, window, floor and roof. All pretty straightforward. Opened the door (there’s a control for that), set up a high-res HDRI, and Bob’s your uncle. Render is a bit noisy (more samples needed?), and it’s crying out for some grunge textures, but I’m optimistic about the prospects.