Systems Manager Job Description?

Having worked in school IT departments for over four years as a senior tech. I have recently been given the new role of Systems Manager covering ICT throghout the school. As the education authority have decided to redefine support staff roles in education we have had to choose a job description from a selection. The role of Systems Manager is not covered so I have been asked to write my own job description and do not know where to start. Can anyone help?