Agreed. I think they mean on the cost for building the building, not the cost per employee housed in the building.
I.e. a closed-offices building might cost $1 billion and house 10,000 private offices with 10,000 employees, whereas an open-plan-offices building of the same area and volume might cost $800 million and house 50,000 employees in a bunch of open areas with a few meeting rooms peppered around.
I.e. a closed-offices building might cost $1 billion and house 10,000 private offices with 10,000 employees, whereas an open-plan-offices building of the same area and volume might cost $800 million and house 50,000 employees in a bunch of open areas with a few meeting rooms peppered around.