Thanks for all the advice! My local hardware store didn't sell thr strips so I bought expanding foam fillers. I was able to fill up a couple of other gaps too so I was very happy with it!
I'm modifying my Craigslist coop and am concerned about weasels getting through the gaps in the roof. The roof is beveled and made out of sheet metal, with regular gaps between the wood and the roof. I'm putting quarter inch hardware cloth inside by the gaps but don't think this is sufficient...