Megillah 5b discusses things that Rebbe did. One of the things that Rebbe was seen doing was planting on Purim; the Gemara retorts that this is surely not allowed as planting is work, which is not allowed on Purim. The Gemara then answers that the reason Rebbe did it was that he was effecting a 'Planting of Joy'. The Gemara quotes a Mishna about 'Planting of Joy' and 'Building of Joy'. The Gemara asks what a 'Building of Joy' is and explains that it's a house for a newlywed couple to do the Chupah. We, nowadays (in some sects of Judaism) don't do anything similar to this, so what is considered a 'Building of Joy' nowadays?