Here are two approaches to modeling a surface with five sides.
The first approach is to model a larger, untrimmed surface with four sides by extending two of the sides, and then trim the larger surface to create the fifth side.
The second approach is to split the surface into two surfaces, each with four sides. The divide between the surfaces runs from the middle of one of the edges of the five sided surface to the opposite corner.
The trimmed surface will usually have fewer control points, The two untrimmed surfaces will usually have more control points in total and requires matching along the coincident edges. The acute corners of the untrimmed surfaces can make matching difficult.
The locations and shapes of the all the edges of the untrimmed surfaces can be directly controlled while the location and shape of the trimmed edge can only be controlled indirectly by modifying the shape of the surface.
Example: FiveSidesDC02.3dm (1.6 MB)