Shulchan Arukh Orach Chayim · Siman 22

English

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. Rem"a: 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)