Unfortunately barn owls are almost gone from the state; they've been declining very badly since the 1940s due to habitat loss (though historically they didn't really have a strong presence here). Now Michigan's remaining barn owls are considered endangered and "functionally extinct" as a breeding population. The last confirmed barn owl nesting in the state was in 1982, and a single owl sighting "yielded possible breeding evidence" in 2002. (Source: Michigan Breeding Bird Atlas II). It's really unfortunate, they're beautiful birds and VERY good at controlling mice. I used to work with one (I volunteer at a nature center with raptors) but sadly he starting having seizures and passed away... he was a cool bird though, miss him a lot.
Maybe screech owl or kestrel boxes could be an alternative? As a bonus, screech owls love eating cockroaches! I do love the idea of inviting natural predators as a way to control pests. Well, small ones anyway, that aren't going to hurt the chickens themselves...