Pallets suck for wood stacking. We used them for years. Ankle eaters, they get filled with debris, lovely highways for chipmunks and other vermin to travel up in the wood and make nests. A few years ago we built a proper lean to with corrugated metal siding. Did the floor with some older rectangular patio pavers we no longer needed. Works great. Also a barrier for woodchucks who love to come up under piles of firewood. Can be swept clean in the spring.
We do use one layer of pallets on top of the patio bricks to stack the wood on, it does allow for better air circulation. We just don’t have to walk on them.