פירוש על בבא בתרא 6:8

המקבל מחבירו – with contract-labor job that he should dig him a grave.

If a man sold to his fellow a place in which to make a tomb, so, too, if a man was commissioned by his fellow to make a tomb, he must make the inside of the vault four cubits by six, and open within it eight niches, three on this side, three on that side, and two opposite [the doorway]. The niches must be four cubits long, seven handbreadths high, and six handbreadths wide.
Rabbi Shimon says: “He must make the inside of the vault four cubits by eight, and open within it thirteen niches, four on this side, four on that side, three opposite [the doorway] and one to the right of the doorway and one to the left.
He must make a courtyard at the opening of the vault, six cubits by six, space enough for the bier and its bearers. And he may open within it two vaults, one on either side. Rabbi Shimon says: “Four, one on each of its sides.”
Rabban Shimon ben Gamaliel says: “All depends on the nature of the rock.”
Mishnah eight deals with the building of tombs.
In the times of the mishnah people were buried in tombs, which consisted of caves with niches carved out of the wall. Each tomb could hold a number of bodies, with one body put into each niche. If someone contracted to build a tomb he must build one 4 by 6 cubits (2 by 4 meters) and make eight niches, each of a specified length, width and height. According to Rabbi Shimon, the tomb must be 4 by 8 cubits and contain 13 niches. In addition, he must build a courtyard over the tomb, big enough for the bier, a stretcher which carried the body and the people holding the bier. According to the anonymous opinion in 3a, the courtyard can serve two tombs and according to Rabbi Shimon it can serve four.
Rabban Shimon ben Gamaliel, section 4, disagrees with Rabbi Shimon and the anonymous opinion in section 1. According to Rabban Shimon ben Gamaliel the size of the tomb is not set in absolute terms, but depends on the nature of the rock. If it is hard rock he is only obligated to make eight niches in a 4 by 6 tomb, but if it is soft rock, he is obligated to make thirteen niches in a 4 by 8 tomb.

ארבע אמות – in width and six [cubits] in length.

שלש מכאן ושלש מכאן – to the two sides of the length of the cave, and two opposite the entrance to the cave, and each grave is four cubits long, and its width is six handbreadths at a height of seven cubits, it is found that between each and every grave from the sides is a cubit-and-a-half, and between the two that are opposite them two cubits.

הכל לפי הסלע – if the place is hard, the recipient is not liable to dig other than six cubits length and four cubits width according to the words of the first Tanna/teacher [of the Mishnah], but if the place is soft and crushed earth, the recipient is obligated to dig [a grave] six [cubits] by eight [cubits] according to the words of Rabbi Shimon, but the Halakha is according to the first Tanna/teacher.