WordNet
n. a garden on a flat roof of a building
Wikipedia
A roof garden is a garden on the roof of a building. Besides the decorative benefit, roof plantings may provide food, temperature control, hydrological benefits, architectural enhancement, habitats or corridors for wildlife, recreational opportunities, and in large scale it may even have ecological benefits. The practice of cultivating food on the rooftop of buildings is sometimes referred to as rooftop farming. Rooftop farming is usually done using green roof, hydroponics, aeroponics or air-dynaponics systems or container gardens.
Usage examples of "roof garden".
Sometimes the smell of the morning bread from the ovens took him to the kitchens, and sometimes he would climb up to the roof garden or wander all alone down Traitor's Walk.
I ate black olives, slices of pale soft cheese and fresh leeks from the roof garden.
I sped off to find Mojo, who was sleeping in the cold wet roof garden as if it were the most normal thing in the world.