Hi there -- what is very likely happening is that the half-gable roof that you have extended through the full gable is causing the game to cast a shadow. Intersecting roofs like that can sometimes trick the game into thinking that your exterior walls are boxed, so it will "turn off the lights" on them, even though they are exterior walls. Try deleting the half-gable to see if that fixes it. (Are you using the auto roof? If so, turn that off first.) If that fixes it, you will want to play around with other kinds of roofs on that portion of the house until you find one that doesn't interfere with the larger gable.
One more quick note: you may want to change the title of your thread to something a little more descriptive, so you get more hits from people who might be able to assist.
