Ceiling insulation

[cabriolethiboy]

I have been a lurker on here for a long time, but this is my first post.
I built a 28 x 32 extension onto my pole building for my shop. I insulated the walls with 2" rigid foam insulation and covered it with OSB. The ceiling has metal siding on it. I have a lot of 2" foam leftover so I thought I might put it in the ceiling. If I do do I need a vapor barrier between the steel and the foam? I am getting conflicting answers on this.

 

[CraigFL]

vapor barriers should always be on the warm side. There will be a temperature gradient across the insulation and the metal roof from room temp to outside temp. The idea is to have the vapor barrier in a place where the water vapor would condense on it(because the temperature is high enough) before it damages anything.