ive built many many steel buildings and have a barn like yours only much larger and i must say that white foam doesnt do much. the best and cheapest option really for this type of building is that spray foam. it really keeps my barn cool in the summer and i can go in there in the winter with out heat and it not real cold in there, not only that it will prevent a condensation problem that you will surely see once the inside temp is different than the outside.