samba - Mar 2015 - Root forest/regional forest set up...

Hi list,

All the docs I've seen use a combined root forest/regional setup, 
whereas I'd like to have separate regional trees under an essentially 
empty root forest.  How does this work?  If it matters, I'll be 
migrating a Samba3 NT-style PDC to provision the regional forest.

Links to relevant docs or any info appreciated.

Thanks!

-John