I’ve had good luck with the Gorilla Glue with the blue cap. Put it on with a toothpick. Whatever you decide to use. You can remove the shell and add something to the underside to re enforce it. This would involve removing some paint to get a good bond. I think no matter how you do it. It will involve some sanding, filling and paint.
My suggestion is to remove the roof, turn it upside down, put the broken piece into exact position, and glue a thin styrene patch to the underside of both pieces using styrene cement or epoxy. That should minimize the visibility of the crack on the upper surface. I would try to avoid gluing in the crack itself which would be visible from the upper side. A small, thin patch on the lower surfaces would not be noticeable if you do it carefully.
MELGAR