The image you supplied doesn't give much information on what we have available to work with. It's therefore difficult to advice.
In general, "all" surfaces are four sided and in the ideal world rectangular. I the real world the rectangularity almost never happens.
Since surfacing is a form of approximation of a desired shape, maybe you need to create some curves that you can use to define the missing surfaces.
A surface cannot guess the shape it should have, you need to guide it into that shape with some curves.
Regards,
Tomas