Sketch - Chair Negative Space

I selected a chair from a magazine that had an open back to the seat, in order to show the shape of the chair in a negative form. As you see, the negative space is shaded in and it outlines the chair. What I would have done differently was to challenge myself by sketching the chair at the same time while shading because what I did was that I sketched the shape of the chair first and then shaded around the chair second.