Gable roof not being generated

[Elovia]

That's a head-scratcher, for sure. It should work as you describe, and if it isn't, then something, some setting, is awry somewhere.

Just a suggestion, but what about building in a temporary garage door that is the width of the two single doors combined, and then use the Gable over Wall/Door tool to define the gable. Does the software still refuse to do it? I tried to replicate the problem in Pro 8 just using Auto Rebuild Roofs, but I think the problem's origins are a function of your building's dimensions (of which I can only guess from the images provided).