Will you be using the space for other activities or just quilting and computers? Do you have a long arm that will require space? How many sewing machines will be placed in the area? How many windows are there in the area? Do you want to sew using light from windows? I'm guessing you will want a design wall and space for a table for cutting and such. How many computers will go in the space?
I know lots of questions but lots of things to think about with new space. Congratulations, I know you and DH will have fun designing and using this space.