If one hollows out a haystack to make a sukka, even though the hay is kosher sekhakh, the sukka is invalid because of the principle of “‘ta’aseh’ – ve-lo min he-asui” (“‘you shall make’ – not something ready-made”). That is, one must make the sukka by laying the sekhakh, and it cannot be made indirectly by hollowing out the area under the kosher sekhakh.
The principle of “‘ta’aseh’ – ve-lo min he-asui” dictates the procedure for building the sukka: One must build the walls first and only then lay the sekhakh. If he reversed the sequence and put up the sekhakh first, according to many poskim the sukka is invalid, because the sukka must be “made,” i.e., completed, by putting up sekhakh, and if one put up the sekhakh first, it is the building of the walls that completes the sukka.
An awning or tarp may be placed above the sukka such that it can be spread over the sukka when it rains and removed when it stops raining, so that all can enter a dry sukka. While the tarp is spread, the sukka is invalid, as the tarp constitutes a barrier between the sekhakh and the sky. Once the tarp is removed, though, the sukka is kosher again. However, if the sukka was built while the tarp or awning was spread above it, many maintain that the sukka is invalid, because a sukka must be made kosher by placing sekhakh, not by removing a tarp or awning (Baḥ; MB 626:18; Rema 626:3 is lenient).
One may fulfill the mitzva with a borrowed sukka, which one has permission to use (Sukka 27b; SA 637:2). If the owner of a sukka is away, and there is no way to obtain his permission to use his sukka, one may nevertheless sit in this sukka, because the Sages assume that a Jew is pleased when his property is used to perform a mitzva. However, if it is known that the owner is careful about who he allows in his sukka, or if there is concern that the owner will return, be too embarrassed to enter the sukka when he sees strangers sitting there, and be upset that they are in his sukka, then one may not use the sukka without explicit permission (Taz ad loc. 4; Bikurei Yaakov ad loc. 4; MB ad loc. 9).
One may not build a sukka on private property without the owner’s permission, nor may one build it on public property if the public or its representatives oppose it. If one nevertheless builds a sukka in such a place and sits in it, he may not recite the berakha, for this is not a blessing, but blasphemy, as the sukka was built through transgression.
. If one builds a sukka on another’s or on public property (such that it is a nuisance to passersby, and the public and its representatives would certainly forbid building a sukka there), he has fulfilled his obligation be-di’avad, since he has not actually stolen anything; the space remains in the possession of its owner or the public. However, since building and staying in the sukka are prohibited, he may not recite the berakha (SA 637:3; MA ad loc. 1; SAH ad loc. 11). In the margins of public property or in a place where a sukka barely bothers passersby, once may build a sukka (as is the accepted practice in many places), because as long as no one objects, we presume that they accept what he has done (BHL 637:3 s.v. “ve-khen”).
If one steals a sukka that had been put up in a wagon, and he sits in it, he has not fulfilled his obligation; since the sukka is not attached to the ground, it can be halakhically “stolen”, and one does not fulfill his obligation in a stolen sukka. One who stole wood and used it to build a sukka can fulfill the mitzva in it and recite the berakha, even though he has violated a prohibition. This is because of the Sages’ enactment (to ease the path of those who seek to make restitution) that one who steals wood and builds it into a house must repay its value but need not demolish his home to return the original wood. That is, the Sages deem the wood to be the thief’s property, with no connection to the original owner. Consequently, one fulfills the mitzva with, and may even recite the berakha on, a sukka of stolen wood (Sukka 31a; SA 637:3; MB ad loc. 15).