I would love to see an option on every window and door (if the door has glass parts) to have regular windows or illuminated ones.
It could be the same method as the color selection: check the box "illuminated" and select the color of the light.
That would be the easiest way to have the windows lit up (and the option to have some windows dark as well, in reality not every room in a building is lit up at night)
Even better: have the option to have windows light up randomly for a certain amount of time, this would be a nice touch of realism if you build a hotel