there's a good article about the convention centre's "living roof" here:
http://www.joconl.com/article/20060508700
excerpt from above;
Bruce Hemstock of PWL Partnership, the landscape architect, said the project team has collected seeds and bulbs for nearly 400,000 plants — mostly wild grasses and grasslike vegetation native to the Pacific Northwest -
"We want a diversity of grasses and plants that will flower at different times, produce different types of seed, and attract different insects and birds.”
A protective layer will keep nature outdoors, and a growing medium 15 centimetres deep will provide a base for the greenery. The sustainable design of the living roof includes drainage and recovery systems that will collect rainwater for irrigation."