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15. May one gather non-Muktzah rocks and use it to build a temporary structure:
For insulating food on Yom Tov for the sake of Shabbos:  When Yom Tov which falls out on Erev Shabbos, it is forbidden to insulate hot food for Shabbos with stones, as it is forbidden to gather stones on Yom Tov, as this is similar to [the prohibition against] building [on Shabbos and Yom Tov].
However, if one has nothing else [available] to insulate with other than the stones, then it is permitted for him to insulate with them, as [by doing so] he is not making a permanent structure, but rather a temporary one, which is only Rabbinically forbidden to be done, and due to the [Mitzvah of] honoring Shabbos the Sages did not decree [in this situation, against using the stones to insulate], being that [in this case] it’s not possible for him to insulate in any other way.
Making oneself a toilet out from stones: Large stones which are organized to create a seat with a hole which one sits on in fields by the area designated to be used as a bathroom, is permitted to be organized on Shabbos, being that [doing so] is a temporary structure that is not made to last, and a temporary structure is only prohibited to [be made] Rabbinically, and due to respect of humanity they did not apply their decree [in this case].
Nevertheless, to make a form of a tent with a roof is forbidden even though it is only a temporary.
Summary-May one gather non-Muktzah rocks and use it to build a temporary structure?
This is forbidden due that it appears like building, However, if one is doing so for the sake of a Mitzvah or in order to relive his bowels then it is allowed.
 Admur 259:6
 Admur 312:15
 Regarding the problem of Muktzah there are opinions that say that this is only referring to stones that have been designated before Shabbos to be used for this purpose. However, others learn that even if not predestinated the Sages allowed one to move it. [Mishneh Berurah 25] [It seems from the Alter Rebbe like the latter as a) Why didn’t the Alter Rebbe mention the case is referring to designated stones, and b) if the stones were designated for this, then the structure made out from them is permanent not temporary.
 Chapter 259 Halacha 6