When to build the Sukkah:
May one build his Sukkah on Erev Sukkos?
Ideally one is to complete the building of his Sukkah prior to 2.5 hours before sunset. If however it is past 2.5 hours before sunset and one has still not built his Sukkah, it may nevertheless still be built.
Is everyone to have their own Sukkah?
It is proper for each family to build their own Sukkah just like each person has his own house.
Building a Sukkah on Chol Hamoed:
One who did not build a Sukkah before the Holiday is to build his Sukkah on Chol Hamoed and dwell in it. This applies whether one did not build his Sukkah due to negligence or due to no fault of his own. This applies even at the end of the seventh day of Sukkos nevertheless he is obligated to build a Sukkah in order to dwell in the Sukkah for the remaining moments.
 Rama 624/5
Ruling of Admur: Vetzaruch Iyun as to why this was omitted by Admur.
Other Opinions: Some Poskim rule one is to build the Sukkah before Yom Kippur in order so its Mitzvah becomes included in one’s verdict for the coming year. Others arbitrate that the walls are to be built before Yom Kippur while the Sechach is placed after Yom Kippur. [Shaareiy Teshuvos]
 Sefer Haminhagim; Aruch Hashulchan 624/7; Kaf Hachaim 624/35
 The reason for this is because one is not to delay the performance of a Mitzvah which he has the ability to fulfill. [ibid]
 Mateh Efrayim 625/9; M”B 625/2 [there he writes past midday it is forbidden, however according to the ruling of Admur one may always be lenient according to the opinion which holds Mincha means Mincha Ketana.]
 As a) It is for the need of Yom Tov, and B) It is for the sake of a Mitzvah. Vetzaruch Iyun from the wording or Mateh Efrayim and M”B ibid, although perhaps they were merely referring to by what time should one plan to have it built by, and not bedieved if one did not yet do so.
 Likkutei Sichos 20 p. 267
 Now although the verse states that one is to build his Sukkah [to dwell in it] for seven days, this does not mean that one has to have a Sukkah built from before the seven days and hence it cannot be built on Chol Hamoed being that there are no longer seven days remaining, as rather the intent of the verse is that one is to build the Sukkah throughout any of the seven days. Thus if one did not build it before the first day he is to build it the second day. [ibid] Likewise one is not required to live within the Sukkah for seven days to fulfill the Mitzvah and rather even if he remains within the Sukkah for only part of the time he fulfills the Mitzvah.