Currently, the wooden warehouse provides 5k storage whereas the plaster version only provides 3k. These structures have the same footprint and appear to be the same size - they should provide the same storage.
Additionally, the large warehouse provides 15k storage, making it significantly less efficient per tile than the smaller versions due to its gigantic footprint. Its storage should be increased to bring it more in line with the other options, preferably even more efficient than them. Currently, the only reason to build it is to have a safe place to keep in-world horses from being killed.