User special sub-category

Hello,
im looking for plugin or “how to”. I have blog with many users and categories. My idea is that user can assign post to a main category (fro example “Cars”) as usually (into this category can add post every user). But also will have options for create his own sub-categories (into this sub-categories can add posts only this one user).
For better explain:

User will write about Audi Q8. This post will be added to a main category “Cars”. And under this main category will be this special only user sub-categories like…
Vehicle Summary
Photos, Videos, Colors
Rebates, Payments, Prices
Standard Equipment…etc

So it will be something like user own blog.

Thanks