You have to remember, the best places to detect, are where many people gathered, for the express purpose of exchanging money (ie.: saloons, stage stops, stores, etc....) or the express purpose of travel (camp-sites, layover camps, stage stops, hotels, etc....) or the express purpose of recreation (beaches, parks, athletic fields, picnic grounds, camp grounds, etc..., etc......) I would therefore think this (old silos or barns) would not,
in and of themselves, be a good area to detect. They were just "work zones", of just a particular set of workers. They are not particularly a "gathering" spot, where multiple people came and went, recreated, slept, ate, played, spent $$, etc..... Also, they are working zones, so will be susceptible to farm junk (iron, tractor junk, slag, wire, etc.....).
Sure, "anything is possible", and sure enough, someone can come on saying they found a such & such at an old barn or whatever. But ratio-wise, to the type takes someone finds at an old-town sidewalk tearout, a beach after storm erosion, a virgin stage stop or picnic site, etc.... it will not compare.
But if you're talking REALLY old barns or silos (1700s or early 1800s) then perhaps it's worth your time to "go into relic mindset" and put up with a large ratio of junk (both old and new) for the chance at a large cent, reale, etc.... Would you want to do that for a wheat penny? Probably not