I assume you've tested some "folder"-like plugins that add some features to be able to organize uploaded files into folders. I think there's no plugin available though that will offer exactly what you are looking for. For the normal files section of an Elgg site every user would have separate folders and it's quite unlikely that any plugin will offer a way to create a folder where all users could put their files into on upload. For such a common folder it's more likely that a group folder is needed, i.e. you would need to create a group on your site and create a folder within the group's file section. Every group member would then be able to add files to this group.

The file_tools plugin should allow you to do what I've just described. Still, it does not prevent non-admins from creating new folders. To be able to stop this you would need to modify the plugin code. For example you could change the code to show the option / the button to add a folder only when an admin is logged in.

Maybe it helps to contact the developer(s) of the "folder" plugins you have tested to ask for advice or suggest some feature (like restricting the folder creation to admins).

@iionly thanks very much for the advice. It worked quite fine. I appreciate. 

I craeted a group into which I placed all teachers, and then I created folders into which they can all post. I am just having hard time changing view of folder files from the default list type to the gallery view (grid view). Hope there's a simple way of making grid view the default file view on the entire site. Any idea?

list type e.g http://elearn.makererecollegeschool.com/file/all  to make gallery view e.g http://elearn.makererecollegeschool.com/file/all?list_type=gallery the default.