I have built decking and have four posts at 2 mtrs High, I want to put a flat roof on. Are the four posts able to take the weight of the roof, I plan to use 4x2 joists using mini joist hangers. I plan to use the same layout for the joists as I did for the decking. Is the timber and joist hangers suitable and using the same layout as the base of the decking. Any help would be appreciated.