Tiled now. I was able to salvage about a third of the tiles used from a previous miscalculation. They still make these "utility room tiles" and they're cheap so I ordered more and although there is a slight colour and size difference, I think I got away with it. Most of the floor will vanish under the layout anyway. The tiles are 30 * 30 cm to give the room some scale. No baby GMs were hurt in the making of this photoshoot:
I wish I could just let rip on building the layout but for now it's still "shared space", though I will be more selective about what non-railway stuff can reside here. For example my tiling tools won't be needed again any time soon, so they can go into the attic for now.
I'm giving serious consideration to reversing the door so it opens outwards. I didn't give enough thought to it when I hung the doors in the basement. Bit of a faff reversing German doors as they are surrounded by expanding foam and this needs cutting away to free the frame.