Because of the camera lens distortion I can't see for certain if the ribs are 90 degree cuts, or are undercuts (look like undercuts).
Those ridges raise all sorts of questions. Do they serve a purpose outside ease of fabrication (90 degrees) or another purpose (back cutting)? Is this item so massive because of the structural weakening caused by the ridges, or does the mass serve another purpose.
Also by distortion I can't guess the size of the door on the far wall. And the rail height. Trying to use those visual cues I'm guessing this thing over 10 feet in diameter.