Framing A Flat Roof
The flat roof corner plan view in figure 1 below shows the basic layout of a flat roof.
The roof joists should be sloped slightly to allow rain water run off. The roof could be built as a gable or shed roof with a rise of 3 mm or more and a run of 250 mm.
Lookout rafters should extend inside the building twice as far as they extend outside beyond the wall plate.
Lookout rafters should be shortened 1/2 the diagonal thickness of the hip rafter. Shorten each lookout 27 mm at 90 degrees to the plumb line if the hip rafter's width is 38 mm.
Subtract the joist spacing from the longest lookout rafter to get the next longest lookout rafter and so on. The joist spacing is 600 mm in the figure 1 below.