Information regarding the roof gap issue:
In a recent build, I had created some single tile "rooms" on the same level as the roof, and where the roof was one tile behind and intersected the wall, the roof wall went missing. Because the roof extended above the level of my "room," the gap was visible. I had to bring the roof forward, so that it passed through the "room" to the other side in order to fill the gap.
Here are some images which display the problem. It occurred with all roof types.
http://i916.photobucket.com/albums/ad5/SFsimpics/Sims4/Building/Testing/09-30-14_10-30nbspPM_zps770cc43e.png
http://i916.photobucket.com/albums/ad5/SFsimpics/Sims4/Building/Testing/09-30-14_10-29nbspPM-2_zps389d350f.png