Include all specific material properties and SRI criteria in your construction and landscaping specifications. Roofing materials are important, of course, but also remember other materials on the roof such as pavers, walking pads, and other roof accessories (mechanical equipment is excluded).

It is best to show the credit math right on the plan: total applicable roof area versus compliant, heat island-reducing roof area.  This makes it easier for the LEED reviewers to confirm compliance with the credit.

Create a roof plan for LEED submittal that clearly indicates the following:

Square footage of the roof surface, broken out to indicate the specific areas of different types of roofing materials, as well as mechanical and aperture areas. 
SRI values, green-roof areas, and slope for all areas.

You'll need to find the SRI value of the roofing materials you use from the manufacturer of the material. The typical values listed in the LEED Reference Guide are reproduced here for reference—but don't rely on them!

There are several online databases that help consumers choose roofing materials. The Energy Star Roofing Product site, for example, lists compliant SRI products. (See Resources.)  

Select the materials for your roof, and revisit your roof surface area calculations to ensure that you are still meeting the requirements for a light-colored, green, or combination roof.  

When a combination of green and light-colored roofs, use the formula below (from the official credit language):

Option 3: Combination Light-Colored and Green Roof 

A green roof can be used as a space to grow local food.

Green roofs create habitat for birds and wildlife and, if accessible, add amenities and learning tools for building occupants.