Build mode: Side walls on roof won't move.

@MiriThePhoenix 

In your first pic, I am pretty sure that the reason that the wall does not go all the way to the edge of the roof at the top is because walls do not extend to the edge of the eaves.  If you draw the upper eave in, then the top of the wall will be even with the roof edge.  

On the 2nd pic, I have no idea why the roof wall is black. It should match the color of the adjacent wall section.  I also notice that the regular wall sections are tan instead of grey.  So, my guess is that it is just the angle of the lighting where it hits those surfaces.  If you switch the time of day, it will probably change to match the walls in at least one time period.  

That said, it's been a while since I tried to use roofs like you are showing and I want to do a bit of testing.  If I find something different than what I've said above, I'll post again.

Hope this helps.