Okay I think I've disected the info and come up with a very plausible guess as to the build a droid figures. Not specifically whom, but what kinds.
Simply put, more Astro droids and Protocol/biped droids. (Biped being the likes of CZ-3 or Death Star droid etc. for instance)
Why? 30 total figures to make 7 B-a-D (Build a droid) figs.
That means 4-5 figures to make a droid.
For the Astro droids that's 2 outer legs, 3rd legs, and body/head combo. (4 total figs to buy to get these)
For the protocol/biped droids-two legs, two arms, body/head combo (5 total figs to buy to get these)
So that leads me further to believe we'll actually get some OT droids from this. A new Silver Protocol droid. Sure it's the same as TC-14, but can be marketed as E-3PO (Bespin protocol droid) As well, we can get the Yellow R5 Astro droid seen on Tatooine. CZ-3, since he's so close to CZ-4.
Now if this is true, then we as consumers can mix and match parts to come up with our own designs as well. So it's a customizer's dream. If this is the case, then I can see this portion of the line being a winning proposition for everyone.