Redoing roof

My husband and i ask discussing redoing our roof. Some roofers say yes go down with decking and felt before putting metal back up and some say no its not needed. How do we know what is best or not? I posted a pic of what is up there now. My husband doesnt see that anything is wrong but i feel we shouldnt see light. Also if the attic light is on at night you can see the light on the outside. I will post a pic of the outside is the main reason we are redoing it. We bought it and within a year all this paint has come off. But goin back we arent sure what to do about decking.