Floating Wall from metal I-beam - which first?

The base plate is installed. [See heading--this is a Floating Wall. --required in CO]



Now should I:



(1) build the framing then setup and clamp to beam, shoot nails to attach the top plate (and thus the entire wall) to beam flange. [This is sort of my preference, but not sure if I'm overlooking something that would prevent this. Then drill hole in bottom plate and pin to base plate.



(2) attach the top plate to the flange (before framing out the wall). Then somehow attach the studs and bottom plate afterward? Not sure how I would proceed after attaching the top plate to the beam since the bottom plate is floating.



Thanks in advance for your advice !