The Jewish Calendar and Holidays (incl. Sabbath): Sukkos: The Size of a Sukka:
How big does a Sukka have to be?
If you can sit in there with a small table, you're probably OK. The exact minimum measurements are in dispute, so try to get
it at least 28 by 28 inches. (See Shulchan Aruch O.C. 634 for details).