Hi,
Regretabbly, security based on document ownership is not supported in Kentico 
CMS. Anyway, it is planned to be implemented in version 6.0. 
For now, I would recommend you to consider using 
Starting alias path property in 
General settings of particular user. It is the starting alias path of the content tree in 
CMS Desk -> Content. If you specify this value, the user is not allowed to browse other sections of the website in the content tree. On the other side, please note that this feature is only intended for better usability and it doesn't ensure security control - if you need to establish access rights for the given user, you should grant him with appropriate document permissions (Properties -> Security). 
Best regards,
Michal Legen