The Mishnah taught: R. Yosi says that if Shimon then fenced in the fourth side, we roll onto him the expenses of the other three sides.

Rav Huna: We roll onto him payment of the cheaper materials used in the other three walls.

Question: Until now we have discussed the height of the wall (that it must be four amos), what about the thickness?

R. Nasa: Since the purpose of the wall is to prevent hezek re'iyah (the damage of one neighbor peering at the other), the thickness only needs to be enough to prevent it.

Question: Since no particular thickness was stated, the Chachamim suggested that even a very thin wall would therefore suffice. However, the problem is that it cannot support a roof, which is unlike the Mishnah?

Answer (R. Yosi bei R. Bun): Although its walls cannot support a roof, it could have strong beams that can support a roof.