Roofs, terraces and balconies are open spaces that give you the possibility to build a real garden. Although you do not own land to plant, you can integrate good planters where your plants grow and simply decorated, get a nice atmosphere in rooftop gardens.
The first thing to look at is if you need to use some ornamental plants like more functional resource. I mean that you may need to do a screen that protects you from the wind or the view from other terraces. If so, good located planters with plants that provide this type of protection: bamboo, cypress, lattice with climbing, etc. Think your intended use of the rooftop gardens and introduces the elements you need for it. If you want to put a dining area, a table and some chairs, if you want a seating area outside looking sofas and deck chairs. You may want an area for children, perhaps with artificial turf or a sandbox. You could even set up a small pool or spa. Finally, some planter incorporates more to put decorative plants. Make sure that all containers are the same material and style in rooftop gardens; visually it is much more relaxing.