There are several different parts of a set of house or building plan: The floor plan or plans, electrical plan or plans, the exterior views or elevations, the basement or foundation plan, a floor framing plan, a site plan. Also included would be: sectional details, kitchen and bathroom cabinet details, Heating Ventilation and Air Conditioning plans (H.V.A.C.), the plumbing plan and isometric, and a roof plan from which we would also create the rafter plan.
The roof plan is sometimes overlooked on some plans but it is a very important feature to a complete set of plans. A roof plan is a view from the top of the house that shows the geometry in flat view of a roof. Drawing a roof plan isn’t a difficult task if you already have a grasp of basic drafting. This type of plan is derived from a floor plan and the exterior (elevations) views of the house.
If you are using a drafting board, it’s a simple matter of placing the completed floor plan or plans under a transparent sheet of paper, tracing the perimeter exterior walls, and then measuring beyond those walls using an architectural scale to where the overhang (fascia) of the house will be. Then projecting lines from the exterior views you can determine where one part of the roof line comes together with the other roof lines in peaks and valleys.
In a CAD system, we would do the same thing as using a drafting board. A line would be drawn around the parameter of the home, and then offset the distance of the overhang. You would then measure to each individual peak of the roof and draw a line representing it.
Then, if the roof has more complexity, valleys, crickets (little roofs that shed water from a possible water or snow trap), and shed roofs would be drawn using the same method. Once this drawing is completed, it can be used to draw a rafter plan showing how the roof system goes together and give us the right geometry to make sense of the roof construction.
Some drafters make their living drawing specialty plans like the roof, electrical, plumbing, and HVAC plans by hiring themselves out to designers and architects. This saves these professionals from having to draw the extra complex items on the plans in order to spend more time designing.