Vapor Barrier for Shed Office

Where is the home/shed going to be located?

What do the shed instruction say? A vapor barrier across the floor would be a good thing to keep any moisture down and under the plastic but a vented space (much like a crawlspace) would be preferred.

What is your insulation schedule for the floor?

Rigid foam across the bottom of the framing would be a good thing if you are going to heat and use this thing.

Located in Tulsa Oklahoma.

No instructions with the shed. It's a Tuff-Shed, so they build it. They will build the frame on grade with steel 2x6. So there is need to keep moisture off the joists really. They will allow me to install a vapor barrier if I want, but they don't seem to be worried about it or offer it as an option. They do offer Tyvek on the walls instead of radiant barrier. I am taking that option.

But I would like to keep it off the floor. So that's why I thought about putting it on the joists before the floor goes down. Especially because the floor will only be 6-8 inches off the ground.

The amount of insulation I could put under there with foam board really wouldn't pay dividends I don't think and could cause problems with drainage etc. Thin foam board is all of what? R-3.5 or something?