there I have set up multisite and am using a form to allow

Hi there

I have set up multisite and am using a form to allow people to set up a new site on the network. The problem is that it sets it up as bbbloggers.comnewsite instead of bbbloggers.com/newsite. Any idea what i have to do to get that / in the middle. I know it is missing from some field somewhere but can not see it anywhere. Thanks