OneDrive , Microsoft's Cloud Storage service for Windows Phone has got a number of updates over the last few months that has bought a number of features with it there by improving it as much as possible.
When asked about offline availability of files for OneDrive on Windows Phone, Casey Penk, Program Manager at Microsoft, had this to say:
"Thanks for the suggestion. We know offline access is important, and we intend to bring this feature to Windows Phone. We don't have a specific timeline yet."
Although there is no launch date yet, but the update will be worth the wait. Microsoft is working on bringing the feature to Windows Phone