I like your coop and believe it is worth the effort to repair/rebuild it to original glory....housing chickens. How about dismantling one side ( rebuilding it later....an open side would help with ventilation and removing debris. After shoveling/sweeping what you can....the HOT steam cleaner sounds like the trick and despite what you read, I would use bleach....TSP.....let it dry and spray the interior with good white house paint...
Happy Hatch'en
Happy Hatch'en