By default, users are not allowed to create chat rooms. However, you can enable this functionality for all users, for a user policy, or for a certain user.
Right-click either the default policy (all users), a user policy (users governed by the policy), or a user, then click Properties.
Select Allow users to create chat rooms.
Click OK to save the settings.
Re-initialize the chat service or restart the Messaging Agent to make the option visible to users.