I would like suggest wall mounted shelves as a beginner level carpentry structure. Any fool who's even looked at a shop class can nail a plank with a few supports to the wall for an ugly but fully functional shelf. They to me therefor feel like one of the first ideas that you'd easily come up with, and one of the first things you'd realistically be able to put together as a beginner. For their function I'd suggest that they'd be a lower level storage than crates, as well as serving as a decor to make your inpenetratable fortress more homely. They would require less carpentry skill and material to build than crates, but would also able to store less. They can only be mounted on a wall, and would occupy less moving space than crates (and can maybe be placed above things like crates and counters). Their function would not be a highly neccesary addition to the game, but they would add to the immersion as one of the things you could realistically put together at a low level. I also think they'd be easy enough to create and implement to justify them not having any large impact on gameplay.
