Premium Members Section of website

The best way to have complete control is to use conditionals in your templates. Look at current_user_can() for specific permissions – or if its simply for being logged in you could use is_user_logged_in(). eg:

if( is_user_logged_in() ){
   // echo product details
}else{
   //echo login form and message
}

That we you have complete control over what is displayed to whom.