When considering a green roof for your home, here are some things to think through first.
Depending on the roof to be greened it may need to be waterproofed, on many suitable structures this has already been done, on others it may be advisable to provide waterproofing, this can usually be combined with the need to provide a root barrier. A root barrier is to keep the roots of the more vigorous plants from damaging the waterproofing. On most roofs some means of drainage will be required, again the need to keep the weight to a minimum is usually a factor. Modern technology has designed products that are suited to both a drainage and root barrier layer that look like miniature egg cups. In addition to have these drainage and root barrier layers it is advisable to construct a full bore drain on the roof with the slab sloping towards the drain.
The choice of the growing medium is a most important consideration. What is required is a very lightweight well drained medium that also give the highest degree of water retention to promote plant growth without becoming waterlogged. Typically a good sandy topsoil is mixed in a ration of one is to one with a good compost.To make the mix even lighter wood chippings could be added to the mix.It is important that fertiliser be applied to the soil during the mixing with compost at the installation stage. For optimal plant growth in gardens with high sunlight areas, fertiliser and compost should be added twice a year, early spring around August and then in midsummer during December. It is essential that this process is then continued for, at least, the first 3 growing seasons after planting.
Have a waterpoint on the roof preferably supplied by rainwater that has been harvested.
A green roof is an ideal spot to locate photo voltaic and hot water heating system as they are easlily mainteained because the roof is flat and stable. These can be screened by planting.