Copied from Wikipedia:
A green roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems.
So, they are putting these up outside the Library at my alma mater. Why, you ask? Well, apparently, green roofs serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, and helping to lower urban air temperatures and combat the heat island effect.
I really hope the area right outside the entrance to the University Library is not going to become a major habitat for wildlife. I guess we'll see what purpose the green roofs actually serve. If you want to research this yourself, here's the Wikipedia page. Have at it. Let me know what you find out. Or better yet, email Mike Carmagnola and ask him. I'd do it myself, but I'm too busy blogging.