A ridgeline marks the apex of each of the three roof sections on this roof plan.
Drawing a floor or a roof on a different plane.
As with designing a floor plan layout the roof must also be considered when establishing the footprint of the house.
This means that you have an imaginary plane cutting through the building at an elevation of 4 feet above the floor.
For each offset angle or change in plate.
In the two examples shown below the wall plans are identical apart from the parapet wall in roof b yet the two roof shapes are quite different as indicated by the roof lines on the plan drawings.
The plan is typically cut at a height of about 4 feet but the architect drawing the plan may cut it at a different height.
Also different architectural styles will use the same type of roof.