Here is a difficult dilemma. Should the west wall be perpendicular to the north and south walls, or should it be parallel with the western perimeter of the land?
The land slightly tapers towards the south, the eastern perimeter running more or less due north south, while the western perimeter veers a little east of south. To maximise solar gain, both for the south facing windows and solar roof, we need the south wall to run due east west, so squaring the box brings the east wall parallel to the east perimeter, and brings the north wall parallel to the south wall and the west wall parallel to the east wall. This will leave a narrow space between the south west corner of the house and the perimeter.
In terms of construction, four right angles makes everything easier. Building with right angles is straightforward, the parts are all there, spans are all uniform and there are no left over bits.
In the end, the West wall runs parallel to the plot, so the building is slightly tapered north to south, perhaps around 7 degrees off the right angle.
