If you read about Holz hausens on the internet or watch youtube videos on how to make them, they will describe how to add wood on the top to serve as shingles to shed off the rain. This usually works pretty good if you do it right. You need to make sure you layer them just like real shingles which is not easy to do. This can be hard to do with real shingles so imagine how much harder it is to do with different sizes pieces of wood that don't sit flat. Also, they talk about placing the wood on the top bark side up to further shed water. This is also a great idea but for me by the time I'm putting the final touches on the top with my "shingles", a lot of times I don't have any wood with bark on it left. Sure, you can leave the bark covered splits aside for the roof but it's hard to know how much you'll need. If you don't estimate enough, you'll be short and the roof will look like a mix of wood and bark. It's not a big deal but it is something to think about.
The bigger issue is when you start to use the wood in the winter. The first logs you remove are your roof! At this point, all of your hard work if now exposed to winter snow and rain! Who wants to collect wood for the fireplace that's coated in snow and ice! If it's earlier in the season before the snow, you end up with leaves inside the pile that invites pest and makes a mess.
Our cover eliminates this problem. It had vents at the peak that maintain the normal convective drying that is one of the advantages of a holz hausen. When its time to grab some wood for the wood stove or fireplace, just unbuckle one or two straps and lift the cover up. When your done, snap the buckles together and your done. No need to figure out how to tie the tarp down every time you touch it or throw logs on top of the tarp that later gets buried in the snow.