Can the roof withstand the weight of a solar system?  
  Yes! The heaviest normal GSE family solar heater weighs totally about 225kg fully filled with water. This weight is distributed in 4 squre meters on 6 legs. The load on each leg is far within the permitted weight on roof stipulated by Ontario Housing Code.
Figure 1. Load and Footprint Dimensions
Figure 2. A solar water heater installed on a slope roof.