What budget? My budget was blown halfway through the coop build, when there were only three walls!
I saved a lot of wood and gave a playhouse a new purpose, and still spent around $200+ on new things- wood, hardware, Home Depot oops paint... Maybe if I hadn't made the coop bigger than the 4x4 playhouse I could have spent less.
A lot of people here on BYC remodel/re purpose an old structure for a coop- dog houses, playhouses, swing sets, sheds, desks, kitchen cabinets... you name it! I recommend re purposing if you want to stick within or near a budget. You can also build a coop with free pallets, but you will still need some extra wood, roofing and paint. Do a couple of searches here on BYC and see what you can find.... there is a lot of information out there! My own coop is under my picture,
(-------------- over there.
I'm a great believer in using a shed as a coop and 200 quid as a budget will give you a bit extra to fit it out (or make a concrete base, which is great for cleaning out). Heres the first page from amazon to give you an idea of their cost.