That's going to make a great coop, and cute too. Start watching craigslist free section, sometimes dog runs come up, along with scrap wood or other supplies. Sometimes they are cheap in the for sale section also. Offer up and like apps can also be great resources for free or cheap. Watch for moving sales too, many times people ditch the dog run when they move. Consider a hoop style run also, that may be more affordable? Read the coop pages to see how others have done their sheds, and what is recommended for ventilation, roosts and nest boxes. Now it the time to educate yourself and collect supplies, so you can be ready for the remodel come spring. And of course, we love to see pics, and can advise, as you go along.