Using line intersections to create a 4-point surface

So I am building a dia-grid structure for a project. The problem is I am trying to create a 4pt surface between end points, start points, and two intersection points. The start and end points are fine. I just cant seem to find away to differentiate between which intersection point to make the fourth corner of the surface out of. Ive tried item lists, shifts, and about a billion tutorials on grasshopper. Basically the last corner always connects back to the previous intersection point and creates a hyperbolic surface.

 The blue is the intersection points and the red are start and end  points of lines.