Acabei de ler uma entrevista que tem a seguinte citação:
When the panel was asked how big the Warehouse actually is, the answers ran the gamut from extremely large to impossibly huge. Joanne Kelly said it was infinite, while Allison Scagliotti suggested it was constantly expanding, much like the universe itself. Saul Rubinek tried for a more prosaic answer, guessing that, since the Warehouse is the sum of all twelve that came before it, it must extend about three miles into the mountain. Jack Kenny suggested the precise dimensions didn't matter - what was really important is that we never see the back of the warehouse, that it continue to go on forever.
Então, acho que é bem grande e não parece ter voltado.