I can guarantee that a Rooftop Terrace garden cuts down almost 40% to 60% heat ever reaching the ceiling. If you have enough cover with smaller plants under larger bushes/shrubs/small trees then there will be a cool breeze around the terrace, provide nesting places for small birds and animals, a pocket of nature in an otherwise concrete heat jungle.

The problem is who can afford to maintain the Terrace garden is the bigger challenge. Constantly checking soil, composting, watering, maintenance and just time+expense is usually beyond a lot of folks.