Q. If someone was placing the schach on the sukka and it started raining and he continued to place the schach in the rain, is that a problem because it may be similar to putting the shach on the sukka when it is covered?

A. Horav Shlomo Miller’s Shlita opinion is that even according to the HaGro’s position, that when it rains the suka is not considered a suka, it would not affect the placing of the schach, since he was only ruling in reference to the compliance of the mitzvah and not the building of the suka itself.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a