Anythings possible
Are you just looking for a script which collects pertinent information which would be used to auto-configure and setup a UBB board for a particular domain/subdomain? Basically, the script would create the proper variable files, and place them in a new directory for this user. In essence, the script automatically builds a working UBB in the users personal domain/subdomain.
If that is all there is, its not too terribly hard. However, its quite a bit of code. Probably 15 - 30 hours of work depending on how elaborate the form interface would be. If your looking for just the bare essentials to get the ubb up and running, assume the conservative.
Question: Would the user who created the ubb be listed as an administrator, and be granted access to the UBB control panel? If so, would the user then need to be restricted from changing files such as the ubb configuration? Locking down a few configuration pages is trivial, however If you wanted to create a fully custom control panel, the chore would become quite a bit more involved.
Feel free to contact me if desired.