Rashi on Genesis 6:16/רש"י על בראשית ו׳:ט״ז

1צהר A LIGHT — Some say this was a window; others say that it was a precious stone that gave light to them (Genesis Rabbah 31:11).

2ואל אמה תכלנה מלמעלה AND TO A CUBIT SHALT THOU FINISH IT UPWARD — Its covering (roof) slanted upwards so that it narrowed at the top to a cubit, in order that the water should run off on both sides.

3בצדה תשים THOU SHALT SET [THE DOOR] IN THE SIDE THEREOF — in order that the rain might not penetrate.

4תחתים שנים ושלישים WITH LOWER, SECOND AND THIRD STORIES — Three stories one above the other: the top rooms for the human beings, the middle ones as cabins for the cattle, and the bottom was for the refuse (Sanhedrin 108b).