bbPress Protected Forums is a new plugin that allows you to set role-based posting restrictions for new topic creation in specific forums. After you install and activate the plugin, you will see a new metabox when editing a forum where you can disable new topic creation for specific user roles.
This bbPress plugin will help you to create a more guided forum experience with set topics open for discussion. Perhaps you don’t want subscribers to have new topic posting permissions until they’ve been upgraded to contributors or authors This plugin will let you do that. Download the bbPress Protected Forums plugin from the WordPress plugin repository.