EDC: Environmental Design + Construction, Feb. 2014, by Richard Heller and Chris Psencik.
http://www.edcmag.com/articles/95450-is-your-building-conducive-to-the-installation-of-a-green-roof

"Despite the potential, installing a green roof is not a decision to be taken lightly. There are several structural and site/location considerations to take into account. The most recent news of a probable green roof collapse at a Latvian supermarket should give one pause. Before allocating the time and resources, facility owners and managers should weigh the pros and cons of a green roof and what to keep in mind during the planning stages."