Hello,
there is no out-of-the-box ready to use action to limit the size of the personal space of a user. You can set a size quota for the user itself so all the content the user owns is counted against that limit and the user can't upload / create more content than this quota.
There is the UsageService (on Java API level) which Alfresco provides that can be used to implement custom quota concepts / behavior, such as restricting the content size on a specific folder tree like the personal spaces of users.
Regards
Axel
