People have always been prepared to pay a premium for their own little bit of greenery in the urban jungle, and a quick glance through the property ads shows that a decent-sized balcony or private roof terrace could add anything from £5,000 to £50,000 to the value of your home.

As city living becomes more and more cramped, there is less space to spread out so people are increasingly choosing to spread up' instead.

The good news is that you don't have to recreate the Hanging Gardens of Babylon or fork out a fortune to have a roof terrace.

A simple layout and basic planting can create a little private oasis, well away from traffic and noise, and often commanding fantastic city views. But because of its location, a roof garden does need some special care and planning to make sure it lasts.

Weight
Obviously, most flat-roofed houses were not originally intended to be topped with gardens, so it is worth getting an architect or structural engineer to check how much weight the roof can support before you begin.

Large quantities of soil are incredibly heavy, so use lightweight alternatives wherever possible.

Try using peat-based composts or mix soil with perlite, small pieces of lightweight volcanic rock that can also help with water retention in containers. Instead of using gravel or stones for draining, styrofoam packing beans can be a great alternative and hardly weigh anything.

Weather
Roof gardens are usually exposed to the elements to a much greater extent than gardens at ground level with high winds, lack of shelter and harsh sunlight.

To protect plants (and people) from the elements, securely fixed natural screens can act as windbreaks and will also give some privacy from any overlooking buildings. Containers and furniture will also need to be securely fixed to prevent them blowing away in high winds.

Water
The high winds and direct sunlight can dry out a roof garden rapidly, so it is likely plants will need watering by hand all year round. Therefore, you will need a water supply on the roof.

But you will also need to ensure there is good drainage as waterlogging could cause problems with the structure of your roof, making it leak or even causing structural problems.

Planting
Choose plants that don't mind exposed areas. Low-growing alpines and sturdy shrubs will do their best to withstand the worst of the elements.

Hardy perennials, ferns, ivy and small conifers should all do well and won't cost the earth. If you have lots of containers, plant some pretty annuals such as lobelia or marigolds, and verbena will give some summer colour.

Just make sure that you water them daily and protect them from really exposed areas of the garden and they should flourish.

For more information on plants and gardening of all sorts visit www.rhs.org.uk