Albert Barnes Commentary Ezekiel 41:8

"I saw also that the house had a raised basement round about: the foundations of the side-chambers were a full reed of six great cubits." — Ezekiel 41:8 (ASV)

The foundations of the side chambers - Therefore, the height of the side-chambers from the floor was six cubits (as there were three stories), which sufficiently corresponds with the twenty cubits that was the height of the temple. “A great cubit” is probably an architectural term denoting the line of junction between two stories, which would be the ceiling of the lower story and the floor of the upper story.