On the metal roof of an Industry Building where you have to walk up on the first floor and then take a ladder to get up on the 2nd floor, on the 3rd Floor you can go out on a roof. There actually you can find some loot.

Today i was able to see through the roof.
I attach some Screenshot, so you can see it.

I believe it happens only in 1st. person, since i have never noticed it before...
I will test 3rd when i will be there next time.