I'm not exactly sure what you mean, are you making a raggy quilt, where you put together (sandwiches- top batting, backing) sew them together & clip the seams?
Generally made using 1/2" seams or larger for clipping. So, you want to sew a 40" strip & a 20" strip together, making a 59" strip for each row?
You can switch ends back & forth, and you can cut 10" off one end & sew it onto the other end to mix it up and so you don't have to worry about any seams lining up... I don't quite know what you mean by a (pattern) ....how wide are your strips? Remember you will lose an inch (1/2" on each side) of finished strip.... If this is what you are planning. If you are doing something totally different I guess I need other information b