For the building owner:  
• Expand roof life by two
   to three times
• Reduce summer air 
   conditioning cost
• Reduce winter heat demand
• Storm water management tool
• Possibly get incentives, 
   earn LEED credits 
• Improve public relations
• Use dead space as a garden

For the community:  
• Reduce stormwater runoff
• Reduce city "heat island" effect
• Reduce smog
• Reduce noise
• Reduce energy demand 
• Improve air quality
• Improve aesthetics

For the environment:  
• Prevent combined
   sewer overflow
• Reduce carbon
   dioxide impact
• Remove nitroge
   polution in rain
• Neutralize acid
   rain effect
• Provide habitat for
   birds and insects