I would appreciate any advice on which type of foam to
use on a newly  erected 30x40  14'eave  1-12" pitch metal building.
Slab is set for hydronic heat, so I had figured on some type of spray
foam, open, or closed .  I have read some posts, but am in a quandary
in regards to leaks in the roof, will they show in closed cell?  I spoke to
a supplier of kit based foam and the sales person said that you would
never use open cell foam on a metal roof because it will absorb moisture
and hold it causing rust.  Right now I don't know what the commercial people
are using. I realize cost is a factor, and don't have ANY experience with foam.
  Thanks

Use a SIP roof, many Kits have that option