If you can find them then plastic pallets are the bees knees. They are 4x4 and I used 4 of them to build a 16ft lean-to for my firewood. Then in the 4 corners and also directly in the middle I put concrete block that's shaped kinda like a pyramid but in the center is a hole cut out for a 4x4 post. Start building upwards and tying it altogether with 2x12s that I had lying around. Set the pitch, add some roof purlins and then steel roofing. The way I have mine setup I can fit just about 2.5 full cord in it.