WOOD definately. Metal acts like an oven in the sun . I would also agree with building it bigger than you originally intend - or make it easy to build onto for later needs.
If your not good at building - 1.) look at prices on pre-fabricated shed kits - and take into account many of them you'll have to add windows, ventilation, and interior designs such as roosts, poop boards, pop door, etc... so take into account the end average of money...Then 2.) contact a local carpenter with your dimensions and needs (example : 4 small upper vents for winter, 2 windows, human door, small chicken door, and tell them its for chickens - so you'll want them to add nest boxes) get an estimate from 1-3 carpenters. COMPARE these prices. - who's more affordable and usually carpenters will build you a better quality building for your buck and save you headache of putting it up, and adding the extras...
OR of course cruise Craigslist and check it out - I recently had found quite a few people who had were selling sheds on craigslist around here - too bad i didn't find these when I needed one - lol.
