Ok, I tried it. There's nothing wrong with the fill-command. I redrew the whole roof and it still gives that problem. The problem seems to be that line screwing wrong. Now it stands perfectly vertical. The problem is that that line bends, so the first fill takes the whole area. If I would first fill the wall and then the roof, the building would look brown. Only thing that's sorted out now, is that the window, the door and the 'open'sign are visible.
I placed a blue priority line where the roof starts, and hoped it mixed the fill of the priorities and the visual screen. That didn't do anything good either. That line's just screwed too. Seems like those lines bend too far to the middle of the screen and stop one pixel too soon.