Image from wallpaper.com
Here's another narrow bathroom with dark tiles. Our bath will run the width of the room just like this so it's useful to get an idea of dimensions. There's obviously a light source directly above, which shows how even dark walls can look OK, and the room doesn't need to feel claustrophobic.
This shows how our ceiling could end up, ie: with sides added to seal off the loft space, which leads up to the Velux. Obviously I'm not a fan of this colour scheme!