The big warehouse store this days are build with metal structure, maybe they could save money by doing this and easy for them to turn it green by installing natural lighting. The metal buildings are ideal for warehouse, big bucks store, warehouse type gyms, even houses. 
In our case we are planning to build our house simple as possible so my husband and I agreed to steel framing. This way it will save us a little bit money that we could use on the appliances and furniture. We are excited but we have to wait for another two years to settles and do the things we need to do before we built our house.