Restrict Page Parents is a lightweight plugin to enhance the user permissions features of WordPress. It changes the option to set a page parent to only show pages owned by the current user. It can also be configured to force users to select a parent page before they’re able to publish or save.
Restrict Page Parents prevents users from adding their own pages under sections of the site they do not own or are able to manage. Users can be confined to their own section of the website, making your site permissions much more secure.
Permissions can be configured for each user role, each individual user and turned on/off based on post types.
You can find out more about the plugin here or on the Github project page.
Screenshots
The plugin options page.
Error that appears when a parent page is required.