Yeah, I'm going to guess that the barn is all timber?? I would mostly just worry about keeping the roof on it and check the bones of it. Make sure none of the old timbers are sagging, cracking, or coming out of joint. Worst comes to worse you could always just tack on some cheap drop cloth plastic on the sides of it.
You might also want to poke around online a bit. there are a few old historic barn preservation groups out there. Odds are there should be someone near you that could at least give you an inspection for what all of the old timbers in it and what would need fixing right away, and might be an extra labor source for when you do go through and reside the barn.