trouble alllowing different users to add different content content types

not sure if this should be a feature request or a support request. I was wanting to allow group owners to be able to add polls, blog posts and events to groups, but restrict normal authenticated users to only being able to add comments and blog posts. Is this currently possible and if so how do i go about doing this as i only seem to be able to make the content types apply to all users and not differentiate between different types of users. If not then is this something that might be added in terms of functionality as it would be really useful? many thanks