Material blend layers

hey guys!
I’m wondering if someone can help me out creating a metal material Rusted pipeline like in the very cool subway reflection demo.
I have take a deeper look at the existing materials within the scene but they are just to many ??? for me to rebuild this material.

I have some problmes with the output function *Output Attribute" i even don’t know if my created node is the same output node like in the layerd materials.
So i tried to use my created function output node and deleted the existing output attribute node i mean i replaced it… MY problem is after deleting the original output attribute the prewiev didn’t shows up like
with the *original output Attribute node" ?