I saw this very interesting vort the other day:
There were many Tzadikim who would give large sums of Tzedokoh Erev Sukkos. Among them was the “Divrei Chaim”, Rem Chaim Tzanzer ZT”L.
A reason for this custom:
The minimum requirements for a Kosher Sukkah is as follows:
Two complete walls of 7 by 10 (7x10 טפחים)
[The width needs be 7 and the height 10]
7 x 10 = 70 times two = 140
The third wall could be even just one טפח
1 X 10 = 10
The Sechach needs to be 7 x 7 =49
The same Numerical value as צדקה
Reb Meir Arik ZT”L asked the Bobver Rebbe ZT”L (I think it was Reb Benzion’s Father. (Reb Ben Tzion HY”D was the father of Reb Shlomo ZT”L) as to the source of this custom. The above is what he answered, and Reb Meir Arik ZT”L was greatly impressed.