Sorry, I wasn't clear. I want to put stuff on a rooftop aligned with the roof instead of the NS-EW axes. After loading the geolocation I go to tools > axes and align the red axis with the roof edge. Then I right click on an axis outside the geolocation image and select Align View. It flips the whole model upside down and looks at it from the bottom.
Like I said, it does this sometimes, but not all the time. I just tried it for about the 30th time and suddenly it worked correctly. I have no idea what I did differently, if anything.
I would REALLY like to know if something I do differently is making the difference (and if so what that is, of course) or if SketchUp is making my life miserable on its own. I have wasted an hour on what should have been a task of a few seconds.