actually when i think about this it would be more convenient to have storage limits per user, So we can say 100 GB for a user and the ability to create 10 Sites.

We cater a lot of users who can create users when we limit on a per site base let say 10 GB and a site is bigger we need to raise the limit for every site in the package. It would be better to limit on a user base, so many sites so many diskspace in total, that way when a site is bigger it doesn't matter and we don't have to reserve a lot of unused space.

Also a soft limit notification would be also nice and easier to implement than a hard limit. Most of the user just needs to be notified and they clean up themselves or upgrade...