Flat roofs can sometimes come into problems with standing water or the deterioration under UV light, particularly if they have been there for years with minimal maintenance up keep. In these situations, it may be good to consider converting to a pitched roof.
A pitched roof conversion can be a more costly option, but can be the best thing for the long-term maintenance of the building.
Pitched roofs allow for better drainage and it helps to keep gutters clear due to the speed the water runs, and can require much less maintenance than a flat roof and last longer. Pitched roofs are able to bear more weight than flat roofing, allowing a wider choice in roofing materials and safer maintenance. They also tend to withstand gale damage as a result of their aerodynamic shape.
Many of the flat roofing systems coming on to the market are likely to last longer than ones from previous decades, and now are likely to last you up to 30 years.