Adam Clarke on Genesis 6:16

A window shalt thou make - What this was cannot be absolutely ascertained. The original word צהר tsohar signifies clear or bright; the Septuagint translate it by επωυναγων, "collecting, thou shalt make the ark," which plainly shows they did not understand the word as signifying any kind of window or light. Symmacbus translates it διαφανες, a transparency; and Aquila, μεσημβρινον, the noon. Jonathan ben Uzziel supposes that it was a precious luminous stone which Noah, by Divine command, brought from the river Pison. It is probably a word which should be taken in a collective sense, signifying apertures for air and light.

In a cubit shalt thou finish it above - Probably meaning that the roof should be left a cubit broad at the apex or top, and that it should not terminate in a sharp ridge. But this place is variously understood.