If it's a pebbled finish, all one piece, than it's the fiberglass roof. I believe it's a composit of fiberglass and plastic, and is very thin. However, don't be afraid to walk on it, I do several times a month to dheck and clean. I just haul a bucket with some automotive car wash, bring up a hose, and fill it up top. Use a soft bristle brush and clean away.
One thing to be aware of is that it may develop small cracks that may get larger and let water intrude. By small, I mean several inches long and very thin. When / if you find a crack, best thing to do is drill a very small hole at the end of the crack. This will prevent it from getting larger. I then take a bit of Dicor self leveling caulk and smear it into the crack, let it set and then put another thin layer of caulk over it. After it sets up I take a small piece of Eternabond and place it over the entire repair. That will permenantly seal it. Trust me, it won't get any bigger and will never leak.
I have done this to 1/2 dozen cracks that developed on my Lexi, and it's a 2012. Once you seal it, don't worrry about it.