I did an indie study this summer that was a full exhibition set consisting of 12 studies leading up to a final 2'x3' piece, done on a wood panel. The entire thing was based on Hiroshige's wood block prints, but the piece itself was very representative of myself, my life, and the time I spent living in Japan. A big part of the project was trying to recreate the woodblock look with oil paints.
The studies started out on canvas, which is what I had originally planned to do the final on. I happened, about halfway through, to do a study on a piece of wood and it redefined how I chose to do the project...and, in retrospect, it was kind of silly to think of doing it on canvas originally anyway, considering the source material.
Studies ranged anywhere from tiny to large. I think the largest was about 9 x 12 with the smallest being 4 x something. All but two of them were done to completion.