Unless you have a source for free or just about free shipping containers, you will spend about double converting one to a usable coop. A used 8x20 container run anywhere from $1000-4000. You will need a torch and welding skills for the alterations. Depending upon where you live, shipping containers are a visual nuisance and you have to make additional modifications so they blend into the environment. More $$.
I'd start all over. What's your budget? Chicken #s? What building skills and tools do you have? Time constraints? Building restrictions and permit?
I'd start all over. What's your budget? Chicken #s? What building skills and tools do you have? Time constraints? Building restrictions and permit?