I'd say the main beams and their supports beams are mostly done, now I'm knee-deep into the hard work : figuring out a plausible way to articulate the rings, and having everything matching : the staircases, the walkways, and the rings themselves.
Once that done I'll do the fun stuff that looks pretty like handrails, pipes and such.
The final version of the tower has 8 such "rings", plus 1 "rogue ring" that has no number and is painted in a different way (I have no idea why). Maybe added later for the shorter Briz 4th stage ?
Again, if you find any technical documentation on those towers, understanding how it works would help.