I'm not sure I've ever seen a video or picture of the actual roof construction, or the interior of the roof structure. There is a construction video at
that shows construction of the walls and floor, and just a bit of the roof construction. It won't answer your question fully, but it is a start. For example, it specifies that the roof should bow UP by 1-1/2 inches from edge to center - not flat or down. And it shows that the trailer is NOT built with a conventional frame similar to the frame in a stick-built house. This will make repair of the roof a bit tougher.
You might query the factury - perhaps they can send some photos. And as previously noted, you might look for posts on this board by MariaG, and visit her repair blog. Lots of good info there.
Good luck.
Bill