Storage seems to always be a challenge at communities, especially in urban communities, where most people are moving to the city for employment or schooling and are coming from a large home in suburban. My wife loves to have storage in her own unit vs. outside (ie. garage). So I would say any extra storage in the unit is always a plus and a great unit amenity. As for charges, I have seen extra monthly on onside storage, and a simply unit premium on units with additional storage inside.
Hope this helps.
Thanks,
Pedro