The Mishnah says "Sukah Shehi Govoihah..." According to the opinion in the Gemara that it's because you can't see the Schah,if a Suka is higher than 20 Amos and the floor was made out of mirors, all you need to do is look down and you see the Schach so would it be Koshar?
Aaron Pacanowski, Melbourne, Australia
The Mishnah does not invalidate a Sukah whose Sechach one cannot see. It invalidates a Sukah that is more than twenty Amos tall, period. You can place mirrors on the floor, you can wear strong glasses, or even use binoculars, it is clear that such a Sukah will be Pasul. Likewise, someone who is short-sighted and cannot see the Sechach of the Sukah that is ten Amos tall will fulfill the Mitzvah. Now let us see why that is.
When Rabah attributes the Pesul to the fact that one cannot see the Sechach (because one is not aware that he is sitting in a Sukah), he is explaining why the Torah invalidates a Sukah that is so tall. In other words, since under regular circumstances, a person sitting in a Sukah that is less than twenty Amos tall can see the Sechach, whereas, if the Sukah is taller than that, he cannot, the Shi'ur Hechsher Sukah is fixed at twenty Amos. Taller than that is Pasul.
be'Virchas Kol Tuv,
Eliezer Chrysler