I failed to emphasize the benefits of the plastic for a shop situation.  It is the plastic that really keeps the drafts out, with the fiberglass cutting the cold contact.  If a person is not willing to seal obvious draft areas, and use heavy and sufficient plastic...........better use foam.

The metal sheeting goes on the inside-side of the building, over the plastic, and is not "tight" enough to prevent airflow.........we did it merely as a spark-problem preventer  and for cosmetic purposes.  Further, the amount of the condensation on the inside of the plastic (the heat side)-------assuming a decent job of sealing the outside wall to prevent concentrated blasts of cold air going thru the gaps in insulation----------should be nominal at worst.

We built a house in the mid 80's--------cheapest items in that construction were rolls of Tyvek house wrap, and lots and lots of insulation---------and I continue to believe such were/are a huge and primary factor in me being able to heat and cool 5000 sq feet for 125-180 per month.

(house has 6 inch walls, ground-water loop system, etc etc..........but I still think the keys were the house wrap and huge amounts of insulation in attic (36 inches by bag count) and sidewalls. )

If I were going to look at building a house today........given the labor costs...........I would look really hard at foam, just due to the constant 24/7 temperature requirements.  But, in a shop, where, as I said before, the variables affecting the heating bill are so unrelated to the quality of the insulation...........tough decision to use the more expensive route.

And........we did not attempt to heat the area above the ceiling, which was what the fellow who wanted to foam the place wanted us to do------he wanted to foam the roof.

Obviously, we could have just foamed the steel that we used on the ceiling, and that would have made things comparable to what we eventually did..........and I don't remember any reason he gave for NOT just doing the steel ceiling-----might have been and I have just forgotten.    So, in reality, one cannot really say that foaming vs conventional would include a factor for heating above the ceiling.