SharePoint Online and Office 365 sites do not provide utilities to view site quota usage and there by preventing users to see Storage Quota consumption of sites/document libraries and files.
This sand box solution provides a graphical view of all files and shows their storage quota usage.
This is a web part implemented using Sandbox solution and hence can be uploaded by site collection administrators on Office 365, SharePoint Online and SharePoint 2010 Sites.
This has been tested on Office 365 and SharePoint 2010 Dedicated.
Upload solution to Site Collection Solution Gallery and Activate.
Add the Storage Quota Consumption Web Part from the web part gallery on a Page and view the information shown in the tree view.