I ended up making this basic room, with some red stone. By messing with the directional lighting, you can make the lighting look nice, and Unreal seems to automatically make things darker or lighter depending on how bright the surroundings are.
Then I thought it would be interesting to have a tower instead of a room:
For the window, I needed to use the split option to get it to the right 5-vertex shape
Got some light leaking though which will need to be fixed