Rhino.FileIO.File3dm model = new File3dm();

            Plane plane = Rhino.Geometry.Plane.WorldXY;
            Sphere sphere = new Sphere(plane, 10);

            NurbsSurface surf = sphere.ToNurbsSurface();

            surf.Points.SetControlPoint(0, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(1, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(2, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(3, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(4, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(5, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(6, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(7, 0, new ControlPoint(0, 0, -15.0));
            surf.Points.SetControlPoint(8, 0, new ControlPoint(0, 0, -15.0));

            Brep brep = surf.ToBrep();

            model.Objects.AddBrep(brep);
            model.Polish();
            model.Write("c:\\file.3dm", 4);