This rack in the photo took me about ten minutes to build, out of materials that I already had laying around. And you will need about 8 nails or screws and a piece of rope or wire about two feet longer than your rack.
Lay out the two length pieces in the location where you are going to be stacking the wood.
They should be spaced apart so the base will be about as wide as the length of the pieces of firewood are that you will be stacking on it. Attach one to each end of the base pieces as shown in the picture. Cut two upright pieces the length that you want the height of your rack to be.
Attach a rope or wire to the tops of each upright as shown in the picture. I like to use a steel wire since it will last a long time and won’t degrade in the sun.
That is the disadvantage to this style of firewood rack, The uprights will only stay up when there is enough weight pushing against both ends.
This is fine for a longer term firewood storage rack, but if you are putting wood in and out regularly, this might not be the best design for you. A tarp or plastic sheet will work, but I like to use metal roofing. It keeps covers the top to keep the rain off, but leaves the sides exposed to open air so the wood can dry.