There is no way to see how much storage space is being consumed by old versions of files and which files they are.

Example:
1) I create a large file at it is 1GB
2) I edit this file substantially and it is still 1GB. The previous version is being retained based on my settings

Q1: Is this file now consuming 2GB of my storage space? (Potentially less if you are using smart de-duplication but give I have modified the file substantially it would likely not have much data redundancy.)
Q2: If this file were one among many, how would I know that this file is consuming 200% of its actual file size through version history?

I think both of these should be made transparent to the user.