Is the information circulating in forums—that writing "in sha' Allah" (God willing) as "inshaa' Allah" (God's creation/building) is incorrect because the word "inshaa'" means creation or building—accurate? And is it necessary to issue an official fatwa regarding this?

The phrasing of "in sha'" differs from "insha'" in form and meaning. "In sha'" consists of two words: the conditional particle "in" and the verb "sha'a," signifying the contingency of a matter upon God's will. As for "insha'," it is a single word meaning creation.

The correct way to write it is "in sha' Allah," and it is impermissible to write it as "insha' Allah." God Almighty directed His Prophet Muhammad, peace and blessings be upon him, to make an exception for God's will, as in His saying: (And never say of anything, "Indeed, I will do that tomorrow," except [add], "If Allah wills.") [Al-Kahf 18:23-24]. This is to seek success in matters when reporting about them in the future. It is also narrated in a hadith (definition) that Solomon, peace be upon him, swore to go around to his wives so that they would conceive, but he forgot to say "in sha' Allah." Only one of them gave birth to a defective child. The Prophet, peace and blessings be upon him, said: "Had he said 'in sha' Allah,' he would not have broken his oath, and it would have been more likely for his need to be fulfilled." This serves as a warning against the pitfalls of mere wishes and turning away from entrusting matters to God.