How to create SAN for end users

Dear Readers,

I work as an IT supervisor where i have been asked to create a storage area network to have the end users access the files thru internet.

We have one of our teams who uses Drop box to upload and download the files across the internet. We have three offices, India,Dubai,Canada.Basically they upload files to drop box for the users who works in those locations and they download files, do some modifications and send them back and go on and on.

Most of the designs/files users shares/downloads are common and when one of the users upload a file, the file will be auto synced to all the users having the drop box access. This way, we have noticed bunch of internet utilization and the files that the users shares/downloads are photographic designs which consumes a lot of data and impacts other users in the network.

I want to build a storage device or a file server where i can put all of their data in one place and they can access it from anywhere across the globe via internet whoever needs it anytime.

we have a Sonicwall 3600 firewall handling the entire network of 150 users currently.

My thought is to build a file/storage server create a NAT policyand Map it to the internet but another thought is HOW?

Any suggestions are much appreciated.

Kind Regards,

Syed Rahman