The building in the screenshot and attached .skp file actually exists, in rural France, and belongs to a friend of mine. Well, most of it anyway, part of it is in ruins which has made meaningful measurements difficult, but I've finally, after much much work, got a pretty close representation of the floorplan. The trouble I'm having is in creating a workable roof. I don't believe, unless someone knows otherwise, that I'll be able to render a roof that runs on the building shape.

The red walls represent the edge of a neighbours property. I'm trying to create a roof that runs from the join of the two red walls to the centreline marked on my right-most wall, with a 30 degree pitch.But no matter what I try, Sketchup won't render the roof :(. I'm desperately trying to get a basic construction going, and I'm comfortable that I can render in all the other missing elements if only I had the confidence that when I'd finished that I'd still be able to get a roof on it! 

All the help files, tutorials, and youtube video's I've found deal with symmetrical shapes. I'm stuck, please help!