A 10" square gives you four 2 1/2" x 10" strips. A Jelly roll strip is 2 1/2" x 42" (with selvedges). You could use a layer cake if your pattern calls for your jelly roll strip to be sub cut into different lengths; HOWEVER you will have to figure out if you can get the same amount of pieces from the four 10" strips you will get from the layer cake piece. Sounds like a lot of work but if you are determined to use your layer cake, it could be worth it for you.