Just to be sure: Are you saying that you have (or will have) 7 strips @7 brown and white HSTs?
Here is one option: After you put the center together decide which direction you want to use as your "long" side. Then plan a 6" border on each long side and applique vines and leaves on it. (You can easily stay in your monochromatic color scheme and use a similar white on white or even a muslin) Then run a 1" border around the entire rectangle with a patterned brown.