Please visit some of the web sites below for more information on cool metal roofs. These organizations are based out of the United States, however the information is relevant no matter what part of the world you're in.
Energy Star
LEED / U.S. Green Building Council
Cool Metal Roofing Coalition
Metal Roofing Alliance
Metal Construction Association
California Energy Commission Consumer Energy Center
Cool Roof Rating Council
Metal Building Manufacturers Association
National Coil Coating Association
Lawrence Berkeley National Lab - Environmental Energy Technologies Division
Oak Ridge National Lab
Florida Solar Energy Center
All sites