Bevor you power wash the walls, cut the power off. Sometimes rats make nests in walls and chew on the cables. If you not sure about the cables, call a electrican to take a look at the installation. Check for signs of rats or mices in and around the shed and set up some poison traps. As long as you don't have livestock on the property, you can work with poison. Once the chicken are in the shed, poison is off limits, b/c of the risk that your chicken eat a poisoned mouse and die.
Control the traps every day. If the rat don't "like" the poisen pads, use some peanut butter... normally they can't resist the smell. After two weeks all rats and mice should be gone.
Open windows wouldn't work were I live and maybe you can finde some
second hand windows. The wire over the windows is a good idea, it helps to keep flyes out. I wouldn't remove the tiled floor. It is so much easier to clean.
Do the cleaning in steps: Dry clean: Sweep or blow dust the room. Scrape manure and accumulated dust and dirt from the wall/floor.. Remove all litter from the floor. Use gloves and a mask. Litter can be added to a compost pile. Sweep the floor to remove as much dry material as possible. Turn the power off to the building prior to using any water for cleaning.
Wet cleaning is done in three steps: soaking, washing and rinsing. Warm or hot water will do a better job getting through organic matter than cold water. You can use a cheap neutral detergent, like dish soap.Soak the heavily soiled areas thoroughly. Use a low pressure sprayer to totally soak all surfaces. Soak until the accumulated dirt and manure has softened to the point it is easily removed withe higher pressure. Wash every surface in the building, ceiling trusses, wall sills and any surface where dirt and dust may accumulate. The washing solution can be either a neutral detergent or an alkaline detergent like baking or washing soda. The hotter the water and better it works.
On the pics the shed seems to be out of metal on the outside. If you have metal surfaces with hard water scale, then you will need to use an acid detergent on those surfaces to remove the scale. Vinegar or Citric Acid mix into the water works fine.
A final rinse immediately after washing is recommended to remove any harmful residues. Mop up puddles as they can rapidly become breeding grounds for germs. Thoroughly air-dry the building. A sunny day helps here.
If everything is dry, you can do the repairs. Spray foam insulation and fine steel wool work good esp. with rate holes.
When that is done, you can desinfect the shed with some lower pressure. You will find disinfectants in your farm supply store (i.e. Sorgene), they are not cheep but kills all kind of germs.
Much work... maybe you can make some "after-pics". ;-)
