How to create blog after member registration?

Hi,

After a user becomes a member, how do they create their own blog/site? If I go to my /wp-signup.php page, it redirects me to the join page, which incidentally has all the membership options again (but not the option to create a new blog), thus kinda going in a loop. Multisite is setup and working fine, as well as ProSites, with Pay to Blog, enabled. Oh yeah, I added a positive blog creation tool for this membership plan.

Thanks.