Obtain the outer surface of the revit component

I want to obtain the outer surface of a steel box component. Since no direct dynamo nodes were found, my idea is to obtain the outer contour of the top and bottom surfaces of the steel box, and then use the surface.byloft node to loft and approximate the outer surface. I did it, but does this surface object seem to not support the surface.pointatparameter node?
image
This is the steel box component model in revit


This is the outer surface I lofted out
The problem is that the surface. pointatparameter cannot work well. I originally wanted to add some colored blocks on the outer surface of the steel box to describe the displacement

Explosion into multiple surfaces can solve the problem

Thank you for your reply. This is a very useful node!!