There are innumerable types of policy documents out there, but really they can be broken down into three major types aligning with the three parties that make an archive, namely:
YOU. THE PATRON. THE STUFF.
Commonly spotted policy documents include Collection Policies, Access Policies, general Policy and Procedure manuals. They may cover all topics for all audiences or be very specific to one of the three categories above. If you are shopping around to help draft policy documents for your archives it helps to search for these at other institutions, save them samples to emulate and start reading for the points that make the most sense to you.
Make sure your policies are clear and easily understood