Summarize:

The potentially intense wind and sunlight will make stronger plants a better candidate for rooftop gardens. Seedlings with these qualities will be more likely to survive the first year. Add shade or windbreakers if you plan to add more fragile plants.  Ornamental grasses, honeysuckles, and magnolias all do well in hot, sunny weather. Make sure you regularly water your plants, even those that are drought-resistant. Plants originating from your state or climate will attract native fauna, like birds and butterflies. They will also adapt more easily to your garden than non-native plants. If harsh winds or heat hits, your plants will be much more likely to survive.  Decorate the garden with bird- or butterfly feeders to attract more animals. Ask your local nursery which plants are native to your area for your options. Large plants will weigh down your roof and leave less room for other decor. Small, ornamental trees and shrubs do well in rooftop gardens when protected with windbreakers and placed in stable containers. Add 2 to 4 trees or shrubs at most to conserve space.  Trim your trees' roots every few years to keep them at a manageable size. Examples of ornamental trees and shrubs include: Dogwood, Japanese Lilac Tree, Crabapple, Star Magnolia, and Jack Dwarf Flowering Pear. Plants with large, supple leaves tend to get shredded by the high winds on rooftop gardens. They are also more likely to suffer winter-burn during the colder seasons. Smaller-leaved plants or pines thrive particularly well on rooftops.
Look for drought and heat-tolerant plants. Buy plants native to your area. Choose ornamental trees and shrubs. Shy away from large-leaf plants.