When I consider "the cost of the buildout", I consider that to be the cost to do the buildout, nothing more. Productivity gains/losses are outside the scope of that.
I.e., the claim, as I read it, is that construction of an open office is more expensive than a non-open floorplan, per employee.
(If you consider that, yes, I think open office is the long-term worse option, and the parenthetical in my comment pretty clearly denotes that.)
> I didn't say it wouldn't cost one penny more than an open office, I said it wasn't wildly different.
This still isn't clear to me. An office is probably, what, 10' square, at least? Google thinks, "The North American office size average is currently 150-175 square feet per employee. Open office spaces for tech companies typically use even less at 125-175 square feet per person". That's considerably more room than an open office floorplan, which is probably closer to 4'x4', maybe 4'x5'.
> So many buildouts go halfway already with the tiny "phone rooms"
My company had 3 of those, back to back to back, occupying what like 30–40 sq ft total? That's hardly "halfway".