i'm still working with WebDav and noticed some things :
when a user doesn't have write privileges on a folder and try to create a file, the error message is really not clear :
when a user doesn't have write privileges and try to create a folder, there is no error message : a folder with parent folder name appear and disappear when the page is refresh :
So I did a pull request with some suggested modification to fix them : https://github.com/ONLYOFFICE/CommunityServer/pull/91
I'm not a C# expert, i try to do my best !
Hope it can help

Thanks,
Yoann