Many years ago, we bought a metal frame and white cotton fabric walls to build our sukkah. The frame stayed up all year, I sewed together several bed sheets to throw on top to make a shade, and we'd often have our Shabbat meals outside on the patio when the weather cooperated.
After a few holidays of getting tired of staring at the plain white walls, I decided I wanted to design something to paint on the walls. First I thought something rather industrious - traditionally on Sukkot (Feast of the Tabernacles), there is the concept of seven holy guests - Ushpizin - who visit the sukkah, one for each day of the holiday. Then I thought maybe to start a bit more simply, the seven species of fruit associated with the Land of Israel, and the four species associated with the holiday of Sukkot.
And then I hit on a family-inclusive, long-term project. Using just one handprint from each family member, we would build a mosaic over the years.
The first year was 2010.