The side rooms surrounding the temple widened at each successive level, because the structure surrounding the temple ascended by stages corresponding to the narrowing of the temple wall as it rose upward. And so a stairway went up from the lowest story to the highest, through the middle one.
Jewish Publication Society of America Version (JPS1917) - Ezekiel 41:7 >And the side-chambers were broader as they wound about higher and higher; for the winding about of the house went higher and higher round about the house; therefore the breadth of the house continued upward; and so one went up from the lowest row to the highest by the middle.