I understand the gemara to mean that if you put schach on top of the 4 poles, that the sukka would be kosher for use on shabbos only and not during the rest of sukkos. if so, how can you have a kosher sukkah. if you put the scach on friday. at that point the sukkah is not kosher, since this sukkah can only be used on shabbos. when shabbos comes, the sukkah should be kosher since the walls are considered proper on shabbos only. however, the schach should be the ingredient that makes the sukkah kosher(taaseh velo...) and not the walls. thank you for considering this question.
sol naimark, Queens, NY
Dear Sol
Thanks for your very interesting question. I would take the following approach. The poles which serve as a kosher wall on Shabbos were physically placed there before the Sechach was, thus there is no problem of Ta'aseh v'lo Min ha'Asuy. True, at the time they were placed there, they did not qualify as a wall, nonetheless when Shabbos arrives it is a kosher wall, and was actually there, before the Sechach was placed.
K'sivah V'chasimah Tovah.
Y. Landy