Gemara

46a - Beraisa: One who makes a Sukah for himself blesses Shehecheyanu. When he enters it to dwell in it, he blesses Leshev ba'Sukah;

If it was already made, if he can add something, he (does so and) blesses (Shehecheyanu now, and Leshev ba'Sukah when he enters). If not, he blesses both Berachos when he enters.

Rav Ashi: I saw Rav Kahana make both Berachos over the cup of Kidush.

56a - Rav: We bless Leshev ba'Sukah, and then Shehecheyanu;

Rabah bar bar Chanah: We bless Shehecheyanu, and then Leshev ba'Sukah.

Rav says that we bless first on the Sukah, for it is the obligation of the day;

Rabah bar bar Chanah says that we bless first Shehecheyanu, for it is more Tadir (frequent; we say it on every festival).

Suggestion: The Amora'im argue like Beis Shamai and Beis Hillel!

Beraisa: Beis Shamai say, (in Kidush on Shabbos night,) first we bless ("Mekadesh ha'Shabbos") on the day, then we bless on the wine. This is because the day is why we drink the wine. Also, the day began before we drink the wine;

Beis Hillel say, first we bless on the wine, then on the day. The wine allows us to say Kidush. Also, the Berachah on wine is more Tadir than Kidush; we always bless first on what is more Tadir.

Rav holds like Beis Shamai, and Rabah bar bar Chanah holds like Beis Hillel!

Rejection #1: Even Beis Hillel can hold like Rav. Beis Hillel bless on wine first because it is essential for Kidush, but one can bless on the Sukah without Shehecheyanu!

Rejection #2: Even Beis Shamai can hold like Rabah bar bar Chanah. Beis Shamai bless on the day first because the day is why we drink the wine. Here, we would bless Shehecheyanu (for Yom Tov) even without the Sukah!

Question (against Rav - Mishnah): On Shavu'os, they say to each Kohen 'Here is Matzah (a share of Lechem ha'Panim), and here is Chametz (from Shtei ha'Lechem).'

Even though Chametz is primary (it is Chovas ha'Yom), Matzah comes first (because it is Tadir)!

Answer: Tana'im argue about this.

Beraisa: He says, 'Here is Matzah, and here is Chametz';

Aba Sha'ul says, he says, 'Here is Chametz, and here is Matzah.'

The Halachah is, we bless on the Sukah, and then Shehecheyanu.

Rishonim

The Rif and Rosh (22a-b and 4:3,4) bring the Gemara on 46a, and the conclusion that we bless on the Sukah, and then Shehecheyanu.

Ran (DH v'Im): The Ra'avad says that if one did not eat in the Sukah on the first night, he blesses Shehecheyanu on the Sukah the first time he eats there, unless he blessed when he made the Sukah. Others say that one is Yotzei with Shehecheyanu in Kidush, just like one can be Yotzei at the time he made it. This is not our custom, for one is Yotzei only at the time of making it or doing the Mitzvah.

Rambam (Hilchos Sukah 6:12): On the first night of Sukos we bless on the Sukah, and then Shehecheyanu. The Berachos are said over the cup (of Kidush).

R. Mano'ach: Mitzvas ha'Yom such as Sukah, Shofar or Lulav overrides Tadir. Even though a Beraisa (46a) teaches that one blesses Shehecheyanu upon making the Sukah, since Rava and Rav Ashi blessed with Kidush, we do the same. The Shehecheyanu covers Yom Tov and the Sukah. If one eats in his house on the first night due to rain or sickness, he blesses Shehecheyanu in Kidush for Yom Tov. The first time he eats in the Sukah he blesses Shehecheyanu, unless he already blessed when he made the Sukah. A case occurred, and the Ra'avad did so. The custom is to bless Shehecheyanu also on the second night (in Chutz la'Aretz), lest it is really the first night and last night's Berachah was invalid.

Question: Even if it was not Yom Tov, he should be Yotzei Shehecheyanu on the Sukah, just like one who blessed when he made it!

Answer (R. Mano'ach): (If it was not Yom Tov) since he erred and thought that this was the beginning of the Mitzvah, he was not Yotzei.

Note: R. Shmuel (in Rosh 4:2) says slightly differently regarding Lulav. It was enacted to bless Shehecheyanu only at the time of making it or taking it for the Mitzvah. If yesterday was Chol, he was not Yotzei.

Rejection (Rosh 4:2): In Ashkenaz the custom is not to bless Shehecheyanu on the second day on Lulav or on the Sukah. The Ri says that the Shehecheyanu we say in Kidush on the second night is because of the day, not because of Sukah.

Hagahos Maimoniyos (200): As long as he is engaged in the Mitzvah, he can bless.

Question: If one made a Sukah for himself, he blesses Shehecheyanu then, but only Leshev ba'Sukah when he enters it. In any case he blesses Shehecheyanu for Yom Tov in Kidush!

Answer #1 (R. Mano'ach): If one blessed Shehecheyanu upon making the Sukah, he does not bless again on the Sukah, even if he was not in the Sukah at the time of Kidush (due to rain or sickness).

Answer #2 (Rosh 4:3): The Sukah is because of the Chag. Therefore, Shehecheyanu for the Sukah exempts the Shehecheyanu for the Chag, even if he blessed before Yom Tov (so then he would not bless Shehecheyanu in Kidush). We find that one who did not bless Shehecheyanu on Yom Tov may bless during the festival.

Rosh (4:4): Some say that on the second night we bless Shehecheyanu before Leshev ba'Sukah because we were already Yotzei Shehecheyanu on the Sukah on the first night. Even if it was Chol, one was Yotzei. According to Benei Ivra, Shehecheyanu applies to the Sukah also on the second night. Avi ha'Ezri says that Shehecheyanu should always be said last, just like when Yom Tov is on Motza'ei Shabbos it is after Havdalah. This is not a proof. We cannot bless Shehecheyanu before Havdalah. If Shehecheyanu does not apply to Sukah, it should come first. One Amora says that it always comes first, and still it applies to Sukah afterwards.

Support (Gra OC 661:1): Abaye and Rava argue about Kidush on Motza'ei Shabbos. If we could learn from there to Sukah, the Gemara would have said that Rav and Rabah bar bar Chanah argue like Abaye and Rava do!

Poskim

Shulchan Aruch (OC 641:1): If one made a Sukah for himself, it would be appropriate to bless Shehecheyanu then, but we rely on Shehecheyanu in Kidush.

Mordechai (769, brought in Beis Yosef DH Aval): Nowadays that one person makes Sukos for 100, it is not proper that only he should bless. Therefore, we rely on Shehecheyanu in Kidush, like Rav Kahana did.

Bi'ur Halachah (DH Ela): If he blessed Shehecheyanu on the Sukah before Yom Tov some say that he does not bless Shehecheyanu in Kidush. It is a Safek Berachah, so we do not bless.

Kaf ha'Chayim (14): The Magen Avraham says that we do not need a new fruit or garment to justify Shehecheyanu in Kidush of Yom Tov Sheni, except for Rosh Hashanah. The Bechori Yakov says that it is praiseworthy to have a new fruit or garment also on Yom Tov Sheni of Sukos (since some say that even if the first night was really Chol, Shehecheyanu exempts the Sukah and the Chag).

Rema: If one did not eat in the Sukah on the first night, he blesses Shehecheyanu on the Sukah the first time he eats there, unless he blessed when he made it.

Kaf ha'Chayim (9): Just like Shehecheyanu in Kidush does not exempt Shehecheyanu on the Lulav because one is not Yotzei Lulav at the time, the same applies to Sukah (if he was not Yotzei then). Others say that it does not exempt the Lulav because Lulav does not apply at night, but it exempts Sukah, which applies at night.

Shulchan Aruch (643:1): In Kidush (on the first night of Sukos) we bless on the Sukah and then Shehecheyanu, because Shehecheyanu applies to Kidush and to the Sukah.

Taz (1): Even though the Beraisa says that one who enters the Sukah says two Berachos, we wait until Kidush because Shehecheyanu also applies to Kidush

Mishnah Berurah (2): It does not matter whether or not the person himself made the Sukah.

Mishnah Berurah (3): If one blessed Shehecheyanu before Sukah, he does not bless again, for it also applies to Sukah.

Shulchan Aruch (661:1): In Kidush on the second night we bless Shehecheyanu before Leshev ba'Sukah.

Rema: This is the opinion of the Rosh. One should follow it.

Magen Avraham (Reish Siman 643:1): Likewise, if the Sukah was already made, one blesses Shehecheyanu before Leshev ba'Sukah on the first night.

Mishnah Berurah (2): If one did not eat in the Sukah on the first day, he should bless on the Sukah first. Some say that we always bless on the Sukah first. We do not protest against one who does so. If several people eat in the same Sukah, all should do the same.