The role of "charge nurse" and the duties and tasks required vary on the unit and the hospital. I used to work on a cardiac floor and more often than not I was the night shift charge. The night shift charge still had to take a full load of patients and our ratios were 1:4. If we were short, they would be 1:5 and usually the charge would still take 1:4 in that situation but I have taken extra patients to help out my fellow nurses. I was responsible for making the assignments for the shift as well as assigning beds if we were getting an admission or a transfer. I had to check the crash carts. I served as a resource person for other nurses on the unit. Some nights I felt like all I was doing was putting out little "fires" here and there...trying to make patients happy, listening to their complaints if they had any, etc.
That was pretty much it, lol. Our dayshift charge on the weekdays was our manager, and they never had a patient assignment unless the unit was desperate and the staffing was poor. The dayshift charge (without an assignment) would round with the doctors in the AM. On nights the doctors typically do not round unless it's early in the evening or first thing in the AM at around 0600 but they never required the nightshift charge nurse to be with them or even the primary RN. I would always try to be in the room when the doc was there so I can listen to what they have to say and to also be the patient's advocate.
This wasn't required of me, but if we were slammed with admissions I would try to do all of the admission data for my fellow nurses. Some nurses would end up having "surprise discharges" or transfers and would end up getting back-to-back admissions, so I would help them in that process. I know what it's like to be dumped on and to have back-to-back admissions, so I try to be as fair as possible to my team.
As for an actual job description, why not do a Google search? Search other hospitals (not necessarily in your area) for charge nurse openings and see what they post as their job description and use that as a base for what you're trying to formulate.