You can use whatever you like and put the block together however you like!!!
I'd like a finished size of 16", so 16 and a half I guess OR anything divisable to make that size! For example, 4 X 8" blocks or two panels of 8"X 16".........does that make sense??
I decided that as I had sent that size to everyone else then I should use that size too! I cut the fabric down to 16 1/2" x 12 1/2" then cut some 2 1/2" blocks from the off cut. Remember way back last year, about November I think, I bought the sample boxes from Moda. This sample of 'Frolic' by Sandy Gervais looked like great colours to go with the brown.
I made a chequer board border for the side of the block and ended up with my 16 1/2" square that I wanted in the first place.
Some raw edge applique...................