Storage Policy

I have an issue regarding a client that is running out of disk space but does not want to buy anymore storage. Does anyone have any documents on storage policies. Such things as cleaning up files that haven’t been accessed in 3-6 months, stuff like that. Also my customer wants me to look at certain applications and and find out how I can trim space from there network. I am currently working on a questionnaire for each application manager to asses there storage needs and habits. This is alos something that would help, if anyone hase something like that.