Vector intersection with surface measurement.

Hi, I am working on a project for school and I'm trying to design a facade for two surfaces that face each other. Since its for a hotel I want to create privacy. My idea is to take the surface normal of the one surface and project them to the opposite surface and measure the angle of intersection and drive aperture openings in the facade. Ideally this would create small openings for when the two surfaces directly face each and the sight line is 90 degrees. 

So far I have been able to get the surface normal of the one surface but I am not sure how I would extend it towards the other surface and measure the angle. If anyone could please help me out that would be great!

Thanks 

Tim