On Yom Tov or Shabbos, it is forbidden to fully create or remove a temporary “roof” whose purpose is to provide any sort of shelter. However, this restriction only applies when there is at least one Tefach (8cm) of airspace in height beneath this Ohel. Therefore, one may use a rain cover without restriction if it lies directly on top of the Schach.
If one wishes to use a rain cover which will be raised at least one Tefach higher than the Schach, or which will be spread below the Schach, one must ensure that it is extended at least one Tefach across the width of the entire Sukkah (in addition to any space taken up by the actual roll) before Yom Tov. This minimal amount must remain open for the entire duration of Yom Tov and Shabbos.
A rain-cover which is designed like a hinged door may be used on Shabbos and Yom Tov without restriction.
When removing the rain cover on Shabbos or Yom Tov, one should ensure that any water remaining on it does not pour onto grass or earth (unless still absolutely saturated from the rain).
When using a rain cover of any type, one must ensure that the Schach is uncovered when it is laid out, as well as at the onset of Yom Tov (i.e. from sunset until Tzeis). One should also remember to open the cover whenever the Sukkah is being used.
On Yom Tov or Shabbos, one may set up a temporary partition for shelter or privacy. One may not do so if it is required to validate the Sukkah, but one may ask a Goy to do so. [This is most frequently an issue when the primary walls of the Sukkah are hinged or foldable.]
