A service such as Google Drive is really quite inexpensive, less than half the cost of a Zoho account, which is also good. With our corporate account, there is no size limit. We can have all of the drive space we need. A very simple version of what you are referring to would be to have a folder on Drive labeled "Customers" open that to see folders for each customer, open any of those to individual customers sites. In each of those third level folders you can store anything you want. Drawings (DWG), PDF's, printed emails, Word docs, invoices, pictures, videos, etc. If you want notes, you can have one document that can always be appended; an on-going diary for that site, or several documents. It is a virtual file drawer that your entire staff (and/or customers) can have access to 24 x 7. You can do the same thing with office 365, but 365 does have a strange 22k file limit. You can have one file that is 10TB as an example, but you may only have 22k files before something has to go.