You can't go far wrong if you buy from the manufacturer, rather than a retailer Bionic. Only one markup on cost price rather than two, so you will get better for your money. Ensure the timber is treated and then seal it outside with Cuprinlol Garden Shades or similar -treated wood is not sealed wood. If it's fixed, not mobile, 16mm cladding should be employed and it should be raised off the ground by at least 200mm - more is better as the chickens will shelter underneath. Ours are raised 450mm.