I worked for a construction project management firm and we kept the pressboard divided files folders for each project.  Six tabs of which I don't remember the exact titles, but I kept a sheet of labels for each tab and always had a few ready made for the next project.  I know some of the titles were Lease (or land acquisition type), geo physical, accounts payable, bank docs (it was construction for BOA), and a contact list was always the top sheet on the left side.  The same for accounts payable I kept a sheet summarizing all bills for the project with a total (from a spreadsheet)

One other thought is to purchase a labeling device of some type either a p-touch by brother or one of the dymo labelers with software.  Either will make your life so much simpler!

Keep in mind that the previous person's method may not have been the best and if mgmt approves you might not have to keep to their system.  (I usually reorganize the filing system with any company I join.)