(Mishnah): If one was Gozel a beam and built it into a building - Beis Shamai say, he must dissemble the entire building, and give [back the beam to the owner];

Beis Hillel say, he gives to him its value. This is an enactment to help penitents.

If one entered a ruin and built it without permission, we estimate for him, and he has the lower hand (he gets the Shevach (increased value) or Hotza'os (his expenditures), whichever is less). If he built it with permission, we estimate for him, and he has the upper hand (he gets the Shevach or Hotza'os, whichever is greater).

If [the one who built it without permission] wanted to take his rocks and wood, we do not heed him.

(R. Yakov bar Acha citing R. Yehoshua ben Levi): This is [an enactment] for the sake of settlement of Eretz Yisrael.

Question (Rav Nachman bar Yitzchak): If one entered another's ruin and unloaded his bundle temporarily and wanted to take it, do we not heed him?! (Also here, why can't he take what he built?)

Once [Rav Nachman bar Yitzchak] heard that R. Yakov bar Acha said that it is due to Yishuv Eretz Yisrael, he said 'this teaches the reason].'

Implied question: (It is proper to build a ruin.) However, if one built in a place that is not proper to build, or planted in a place that is not proper to plant [what is the law]?

Answer (Rav): We estimate for him [and he has the lower hand], but we may scheme [to induce the owner] to enter in summer [for shade] and in winter [to escape the rain. If he does so, this shows that he is pleased with it, and the builder has the upper hand.]

Question (to Rav): [Why do we scheme?] It was taught that we estimate for him, and he has the lower hand! (We explained this like MAHARA FULDA.)