Solar panels installed on flat roofs are generally tilted upwards towards the sun to capture more light and prevent the accumulation of dirt on the surface, however this also increases aerodynamic forces from the wind. Installing solar panels onto flat roofs while maintaining weather-tightness and providing sufficient hold-down against wind is critical. Make sure you're talking to the experts.
There are two approaches to fixing down, either adding weights to the solar panels to prevent them moving in the wind or fixing the panels to the structure below. Each has advantages and disadvantages. Whichever approach you favour, Viridian Solar has developed flat roofing systems for simple and rapid installation.