hello I am building a house in Las Vegas (CZ-3B). 

is it cost effective going to an unvented attic using closed cell 
spray foam underneath the roof sheathing for insulation , versus doing a vented attic with a radiant barrier under the roof sheathing with batt insulation on the attic floor?

I assume the unvented attic with be more efficient as the Hvac will be located in the attic, but just not sure if the efficiency is worth the extra costs.