Siman 641

Even though this is a positive commandment to make a sukkah, nevertheless, one does not recite the blessing at the time of its making, "Who has sanctified us with His commandments and commanded us to make a sukkah," as one blesses over milah and over pidyon haben. And the reason would seem simple: for they did not institute two blessings over one mitzvah. Therefore, regarding milah and pidyon haben—this is their blessing. But regarding sukkah, where there is another blessing "to sit in the sukkah"—they did not institute an additional blessing. And this is the reason for tzitzit, and tefillin, and shofar, and lulav, that one does not recite a blessing over their making. However, in Menachot (42a) other reasons were given for this. One: since even a sukkah of Ganbach is kosher, if so, we were not commanded regarding the making of the sukkah. And another reason: because this is not the completion of its mitzvah, for the completion of the mitzvah is in its sitting, and therefore then one must recite the blessing "to sit in the sukkah." (And one can bring this reason close to the reason we explained, see regarding this. And be precise and you will find it easy.)

However, in the Yerushalmi Berakhot chapter nine, and chapter one of Sukkah (Halacha 2), it is stated: One who makes a sukkah for himself says: "Blessed... who has sanctified us with His mitzvot and commanded us to make a sukkah." For another: "to make a sukkah for His name." When he enters to sit in it, he says: "Blessed who has sanctified us with His mitzvot and commanded us to sit in the sukkah." And it is to be wondered: for previously it says there that a sukkah of Ganbach is kosher, and how can he bless "to make a sukkah"? But it seems to me that the Yerushalmi follows its own reasoning: that in an old sukkah one must innovate something in it for the sake of the mitzvah of sukkah, as I wrote in siman 636, and the same law applies to a sukkah of Ganbach. And our Shas, which did not require one to innovate something in it as I wrote there—therefore it did not require a blessing at the time of making. And the Yerushalmi, which requires some innovation for the sake of a sukkah of mitzvah—requires one to bless at the time of making. And we maintain according to our Shas.

However, the blessing of "shehecheyanu" at the time of making—is required both in our Shas, and also in the Yerushalmi there, and also in the Tosefta at the end of Berakhot, see there. And that which they did not require at the time of making a shofar—is because it is for many years. But the sukkah—most of it is made every year (Magen Avraham). Nevertheless, our custom is not to recite the blessing of "shehecheyanu" at the time of making, but rather we arrange it during the kiddush, when we recite the blessing of "shehecheyanu" over the Yom Tov, and automatically through this one fulfills the obligation of "shehecheyanu" for the sukkah.

The Tosafot and the Rosh wrote that if one recited the blessing of shehecheyanu at the time of making the sukkah—he does not need to recite it during the kiddush. And this is a wonder: for the blessing during kiddush is on account of the Yom Tov. And it must be said that they hold that the shehecheyanu of Yom Tov is also exempted before the festival, since he is making the sukkah for the sake of Yom Tov (Beit Yosef). And if he did not eat in the sukkah on the first night, even though he recited shehecheyanu in his house during kiddush, nevertheless, on the next day when he eats in the sukkah—he must recite shehecheyanu over the sukkah, if he did not recite it at the time of its making. And there is one who disagrees on this (Bach in Responsa siman 132). And the primary view is like the first opinion. And if he also did not eat in the sukkah on the first day, when he recites kiddush in the sukkah on the second night—he recites the blessing over the sukkah and afterwards shehecheyanu, as on the first night. And the details of this law will be explained in siman 661: whether the blessing over the sukkah is first and then shehecheyanu, or shehecheyanu and then the blessing over the sukkah, see there. (And see Sha'arei Teshuva subsection 2.)