Siman 22
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א קָנָה טַלִּית וְעָשָׂה בּוֹ צִיצִית, מְבָרֵךְ שֶׁהֶחֱיָנוּ דְּלֹא גָּרַע מִכֵּלִים חֲדָשִׁים: הַגָּה: וְאִם לֹא בֵּרַךְ בִּשְׁעַת עֲשִׂיָּה מְבָרֵךְ בִּשְׁעַת עִטּוּף רִאשׁוֹן (מַיְמוֹנִי וְנִמּוּקֵי יוֹסֵף):
1 Containing 1 Se'if: One who buys a טלית and makes ציצית strings for it should say the blessing of Shehechiyanu, because it is not any less [important] than new vessels. Rema: If one did not say the blessing at the time of making it (ie. completing the טלית by affixing the ציצית to it), he should say the blessing the first time he wears it. (Maimoni and Nimukei Yosef)