I have a 9x9ft Plastic shed that was used for storage. I have 11 heritage breed chicks at 3 weeks old (plan on processing the Males at 8 weeks) was planning on using the shed as a coop. While I was cleaning it out, I discovered a dead rat & a stockpile of palm tree nuts. What precautions do I need to take before turning into a coop?
Palm tree nuts.... sounds like they have a ready source of food already but they will prefer the chicken feed. I am not privy to the nutritional value of these palm nuts but you can bet they are sufficient in protein and carbs and fats being that they are a nut. So, you need to focus on keeping them out of the coop and your expensive feed.
Plastic offers zero protection so focus on getting the bulk feed in metal drums with tight lids and cleaning up any pathway that the rats can use to travel between the food, cover, and any water sources. You want them out in the open so the natural predators can get some of them. Usually I'd suggest a treadle feeder but you might try going without one at first. Just watch your feed consumption, a quarter pound of feed per day per hen, ignore roosters unless you have a lot of them (once you have the male birds processed of course). If you start feeding more than that you have a feed theft problem.
At three weeks old the chicks are at risk from the rats. If you can budget it, wrap the entire coop in hardware cloth and like others have pointed out, bury it deep in the soil because they will dig under it.
Remember that rodents are after one of four things, food, water, nesting material they can shred, and safety/peace and quiet. Very little will prevent rodents from coming after these resources so avoid he silly advice for things like mint, moth balls, predator urine, baking soda, and the like. Focus on keeping the rats hustling for a living from natural foods and away from your feed.