Better access control for designers

We'd like to restrict designer access so users cannot create folders/models but can edit existing models. We find users are creating things in the wrong place, in the wrong type of model, where the processes are not part of a master list. All of which increases the risk of users duplicating something already in existence. More flexibility e.g. using 'CRUD' would help modellers get on with the job but reduce the risk of them creating the wrong thing in the wrong place.