First, the building's build platform is separate from the building so when you build a building and the angle of that building changes but not the build platform. I remedied that problem by making a building's build platform part of the building, then changed the build-angle in the fbi to 65000, since zero is default. Also, if the build angle is changed in the fbi to a angular degree like 65000, the building will not just build at 65000, but will randomize the building's angle from zero to 65000 so you would have all sorts of angles.
The building built most units fine at angles less than or equal to 90 degrees. Also, if a unit's footprint was greater than 3 and the build angle was greater than 45, larger units such as catapults could not be built. In addition, at angles above 90, the building could not build a unit. And most important of all is that most buildings look ugly if not facing front due to missing polygons on the rear. My answer would be that the building's yardmap controls the building so you would have to fiddle around with that until you have a solution.
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