If you look closely at the large white expanse in Google Earth you'll see that this isn't the roof of a building but a large parking area. Actually it is probably an outside storage area rather than parking. The access to the lot is from the back door (probably for forklifts?) of the small L shaped building in the upper left corner of the lot. You can see that as an afterthought they needed access to the lot other than just through the building by looking at the dirt ruts/tracks going out of the NW corner, around the buildings along the water and out to the road.
You'll also see the tall light fixtures regularly spaced throughout the parking lot.
I think the accumulated debris is from the destroyed L shaped building and the storm surge. Similar debris accumulated across the channel to the west.