Smaller buildings are easier to keep comfortable, cost less to run.
Complex shapes are inefficient because of larger perimeter area - see our article on Building Shape
In complex shapes heap roof can result in many ridges and valleys, small sections running at an angle increasing building cost. Even if the shape is simple the individual roof sections run at angles making less room available for solar. Consider using gable or skillion roof to maximise the roof area for solar panels
Make sure there is enough roof space for large solar system. Maximize roof area facing North, also provide some to the West and East
Ensure wet areas are all clustered together on each level and close to the hot water system. This will avoid wasting time and water while waiting for warm water to arrive at the tap. Also cheaper to build - less water and waste pipes to run.
To be continued...
Orientation of rooms
Eaves and shading