Edit Role User in Admin Panel that can add only specific custom Pages

I have tested the main function of Grav, but i can’t find a way to assign to user group a specific function to create a custom page (like Item or Post) without give access to all other content.
I have tested different plugin, but i haven’t find a useful solution.

Basically I just need a custom form to create pages of one type in a specific directory. Possible that it is so complicated?