An enlarging - The “wall for the side-chambers” had for the ground story its full thickness of five cubits Ezekiel 41:9 - then it was diminished one cubit, so as to form a ledge whereon to rest the beams of the floor of the second story, and again was further diminished one cubit for the floor of the third story. Thus there was an “enlarging” of the second story of the chambers by one cubit, and of the third story by two cubits beyond the breadth of the chambers on the ground-floor.
A winding about still upward - Winding stairs led “upward” from one story to another.
The winding about of the house - A collective expression for the various winding staircases to the side-chambers which extended on the north, west, and south sides.
And so increased ... - Rather, “and the lowest story was such that one went by the middle story up to the highest.” The winding stairs were not visible outside, so that one could not go to the upper story without passing through the middle story.