I would recommend an underpayment with vapor barrier just to give it a little bounce. 

Have them quote shingles, tarpaper, vapor barrier, flashing and any valley, material,  etc.  

I also don't see any vapor barrier in your detail.

(The first thing that occurs to me is an "herbal" dispensary, but that's just because I have an unusual sense of humor.) 

I'm sure this would negate the need for a vapor barrier?

Something caused the gas vapor to ignite and the kitchen went up in flames.

Stairs add an extra $10-$13 per step plus Sq ft and 30% waste.ENTRY LVP / Laminate: $7.85/Sq ft with vapor barrier underneath.

Do you have a proper vapor barrier covering the soil?

Recently moved to FL and will rehab my first house in this climate.  1,200 sq ft house with 0 exterior wall insulation and NO vapor barrier. 

@Adam DrummondAdam, your profile tells me you've been in the business for a bit, but still, word to the wise -- respirator with organic vapor cartridges is a must when working with oil-based poly.