I'm a little confused. Not sure exactly what you mean by "steel pole barn" and why would having one have an effect on being under insured? That's something that could happen with any type of building.Perhaps my experience will be of value.
Last month 2 trees fell on my old pole barn my dad built himself in 1961. Now that pole barn was built with used telephone poles and corrugated galvanized siding.
My insurance co. totaled the barn and told me replacement cost is $55,000 for a 48'x36'x10' size today.
Which meant, I had that barn severely under-insured. They sent me a check for $18,900.
So to me, that steel pole barn would be my choice today.