Make simplified External Surface from Self intersecting surface created with T splines

Hi there, I’m wondering if anyone can help me out with a surface I created in Tsplines, Im looking for a way to make the external surface into one polysurface, and get rid of the internal intersecting surfaces. I made the surface using Tsplines, and am wanting to use the form to create a roof shape?

I have tried using shell, and cocoon and converting it to a brep in grasshopper but cant seem to get it working. I’ve attached the file.

roof topology.3dm (1.6 MB)