Thank you..
Yup, your new found coop is pretty nasty. Perhaps @aart has some insight of how long certain disease remains active as, I saw dried runny poop on those high roost and I'm wondering if blood was in that mess. I would don my gloves, googles and mask and take a stiff brush to that...
WELCOME TO BYC. WE are Egg-cited you joined us. As you have come to the right place for all your questions.
For me, it depends on how gross your new found coop is. I'd wear a N95 mask and googles. Then I'd scrape it and use a shop vacuum to suck up all the yuck.
Then I'd use a lot of Permethrin...