Thank you guys for weighing in. I think I am going to start with removing the areas with the mold and see if any learnings come out of that.
I was thinking about using a stud finder to locate the metal ribs as well. I really just need to know where they are to install a sky light, as well as, installing mounts for my solar.
I agree it would be a pain to remove all that, but if that plastic honeycomb has a low R value, maybe I should... I'll start with the mold.