Commercial flat roof advice needed. Picture attached

[Adam Craig]

Going through negotiations on a commercial office building. The agent said the roof needs replaced and my knowledge of commercial flat roofs is pretty minimal. I took some pics and measured it - its 4000 sq ft. Before I call around roofers I want to know what I am talking about. What type of material is on this roof? Its not the same stuff we use on single family flat roofs is it? What are options and approximate costs for replacement? Do they tear it all out or go over?   Thank you!