Ive only been in one datacentre that has anything but a tin roof. This one has a concrete slab roof. It used to belong to a bank before my previous employer took it over, so Im guessing they spent a bit of money on it since it also had other ridiculously expensive things like stainless steel and copper piping for water to prevent corrosion in the cooling systems.
Off topic: I remember the network ops manager telling me about the printers that used to be installed there when the bank owned it. He said "forget about pages per minute and think more in metres per second." Use your imagination to work that one out.