Advice on How To Develop A Customer Service/Support Policy

I have been tasked with the responsibility of creating a customer service/support policy for our IT department. My manager would like it to consist of the areas we support (hardware/software), the expected turnaround time our customers should receive (based upon type of issue), and what is supported after-hours. He wants our customers to know the level of suport they will be receiving from our team. Basically it will be similar to a service level agreement between our IT department and the different labs we support.

Has anyone gone through this process before? Can you advise some good resources to help me get started with this task?

I appreciate any assistance you can provide me.

Thanks,
Craig