Not bad.
Flat roof with edge trim.
Just remember a flat roof might tend to hold water and bow down over time and heat. If you're going to have trim around all the edges and they stick up higher then the roof surface you're making a showell swimming pool.
Hinge location.
Most people like to set their camper level or even a bit tongue up for better sleeping. If you roof is flat and the sides walls has trim on then, and your nose up a bit, the water will slowly collect and head to your hinge area. With the hinge running the width of your camper edge trim to edge trim the hinge itself makes a dam to collect water. Make sure you think about where water can run off.
One suggestion is to start the slope your backshell of the camper downward, then placing in the hinge after a few inches, so the water starts rolling downhill and does not set.
It is hard to explain, so here is a Pic of how the a guy made my teardrop. examples not to follow. Even though the front puddle can drain out of the gap it still takes time. The pool in the back has no place to drain My TD being wood and varnish, water setting for any length of time is bad. If it rains I have a PVC A-frame and a tarp I place on top of the camper.
