multisite custom sign up page and build a site on sub-domain

It appears the same question had been raised before.I read the old posts, but could not get this straight-out, wondering if there is any updated solution to this. Basically, we'd like to get the similar sign up page as here:

http://gyazo.com/52c3e502d7c9e32f6706175bc29b18e7

User can sign up with user name, password, email, and choose "yoursitename.activewebpro.com", which will automatically set up trial website for user to try in subdomain "yoursitename".

Any insight would be greatly appreciated.

Thanks,

Jason