WordPressMU with private sites

Hello everybody,

What would be the best way to achieve the following functionality on my WP network:

-User #1 comes to my main site at abc.com and registers his own site at abc.com/user1. Then user #2 comes to visit abc.com/user1 and wants to register for that site. While the user #2 registers, he gets username and password for the whole network, but in order to access abc.com/user1 specifically, he has to “ask” for a permission from abc.com/user1’s admin (user #1).

– User #2 is now a member of abc.com/user1, but if he wants to access user #3’s site at abc.com/user3, he has to do the above again. At the same time, he has the user rights for the network itself and can register his own site if he chooses so.

I tried to be a specific as I could and hopefully you understand what I’m getting at. Any help, recommendations or suggestions are welcome.

Thanks.