Grab some old 2x4s or 2x6 and rip them to 2x3s and built a retangular box frame about 3' tall. Remember you need 10 sq ft per bird when you're deciding how big to go. Cover the top, one end and a couple of feet on each side of the end with plywood, and hardware clothe the rest along with skirting it. You can use tarp, weather permitting and if you wire the whole thing, in leiu of plywood. Simply anchor a branch for a roost in the sheltered end and nail a old wash pan or box with low sides to the side of the sheltered end sitting on the ground, for a nest box. You have just met the basic needs of chickens. Hinging the end board or cutting in a hinged flap will let you gather the eggs and attaching a couple lawn mower wheels to the heavy end will make it easier to move.