In an Urban Area people are in short of space for gardening. If you find that you are running out of space for gardening Roof Top Gardening could be the best alternative for you. Rooftop gardens also make the best use of frequently unused and wasted space.
Check Building Codes of Your Area
If you going to create the garden in a rental space make sure that your rental property owner doesn't have any problems with the roof top gardening. Moreover sometimes you may face local ordinances against local roof top gardening. In most cases it's not a problem. You also need to notice that if the roof is designed well enough for roof top gardening. You may need to discuss with the expert/architect to ensure that it will not make any harm to the roof surface.
Design Your Garden
Three things needed to be considered before you start - Wind, Water & Light. Normally a Roof Top Garden is more windy than the normal one. If you are going to plant some wind sensitive trees, the architecture of your garden must consider this & of course you need to think about wind breaker & its position.
You should have a proper plan of watering the garden. Lack of proper extraction of water may cause a lot of trouble to your space e.g. permanent damaging the roof, Mosquito & other insects from the dam caused by the non extracted water.
Depending on your plant your garden will need as much as six to eight hours of sunlight. If your building faces some light obstacle from another building then avoid the obscure part of the roof & select the lightened part for better garden result.
Choosing shrubs, ground covers and even trees that will grow is an important consideration in the design of a roof garden. Due to the need of a light weight soil, planting depths are usually between 100 and 300mm in total. This is not adequate for many larger shrubs and most trees to grow in. Generally shallow-rooted plants, ground covers and grasses are the species that are used for a roof garden. Trees can be incorporated and are usually cleverly hidden in below ground containers with increased soil depth or large planters above the soil level and placed at the junction of supporting beams in the roof for added weight bearing support. Also, certain plants do not thrive in the more alkaline grey-water irrigation systems and it is not recommended for food crops, due to the high alkalinity of the water. Special consideration must then be given to the plant species and whether they can adapt and thrive long term in a roof garden. Harsh sunlight, lack of shade and high winds are also often prevailing factors that come into consideration when choosing the correct plants on a roof. Specialist advice from a Horticulturist is usually recommended when designing your plant palette.