The Dimensions of Window Glass for a Trapezoidal Opening

Recently, I received a request from a local window manufacturer for help in determining the dimensions of a window to be manufactured for a trapezoidal rough opening in a house under construction. The rough opening dimensions were known, as well as the roof pitch (riselrun), which determined the slope of the upper edge of the window. The window had to be constructed so as to allow a narrow constant margin around the perimeter between the window and the rough opening.