> parking lots I've seen around LA seemed to have an open top floor That would more commonly be called a parking garage or structure, a parking lot as referred

> parking lots I've seen around LA seemed to have an open top floor That would more commonly be called a parking garage or structure, a parking lot as referred to in the article is just an open, paved area of ground. I suspect the construction issues for the top floor of a parking structure are different from those of ground-level installation with no existing vertical structure. Also, by their very nature, parking garages most likely have significantly less square footage on the top floor than a parking lot for the same number of vehicles.