משנה אויף ויקרא 23:42

A sukkah which is more than twenty cubits high is not valid. Rabbi Judah validates it. One which is not ten handbreadths high, or which does not have three walls, or which has more sun than shade, is not valid. An old sukkah: Bet Shammai invalidates it and Bet Hillel validates it. What is an “old sukkah”? Any one which he made thirty days before the festival; but if he made it for the purpose of the festival, even at the beginning of the year, it is valid.

If one makes his sukkah between trees, so that the trees form its walls, it is valid. Those who are agents to perform a mitzvah are exempt from [the obligations of] sukkah. People who are sick and their attendants are exempt from [the obligations of] sukkah. One may eat and drink casually outside the sukkah.

Women, slaves and minors are exempt from the [commandment] of the sukkah. A minor who no longer relies on his mother is obligated in the [commandment] of the sukkah. It happened that the daughter-in-law of Shammai the elder gave birth and he opened up the ceiling and put skhakh on top of the bed[posts] on behalf of the minor.