I do not mean to seem vague - but it is up to you. If you are comfortable with a 2 1/2 strip (finishing 2"), then work with that. Your center square will start at 2 1/2". If you are ok with skinnier, then use a 2" strip and end at 1 1/2". I personally prefer the larger to work with. Then make the blocks as large as you want. Typically they will have 12 strips - but do what you want. And then adjust your border numbers and size to finish it at the size you want. I agree that Ms. Burns is the queen of strip piecing and you will get a lot of help from her books - but - it is your quilt, make it as you will. I am currently doing the curvy log cabin where one side is 2 1/2" and the other is 1 1/2" and it makes it curve. No one would have ever done that years ago!