I built some wood stacks which have two 8'x4x4 across the bottom (provides air space under the wood, and if really careful I can move the whole stack with a tractor if necessary), some 2x4 attaching them to each other, 2x4's going up and around basically making a box frame. Corrugated metal as a "roof". Keeps the majority of the rain off of the wood under them since the metal panel is wider than the stack of wood underneath. I have these wood stacks a couple feet apart, so if there's a wind the metal from one helps the one next to it to some extent.
If you're relying on having really dry wood during the winter, a basic metal roof like this helps some but the wood definitely still gets some rain on it here and there, a lot less than without but it's not like a tarp or a large roof.