Shoot!!! Sorry Beth, I didn't check this post again until now!
Here's what I would do: If you're making the large pattern, you'd need 50 stitches for the front and 50 for the back. So I'd cast on 50 stitches, place a ring marker [size=2](or whatever you have,m i always lose them and use a piece of contrasting color yarn tied in a loop) [/size], then cast on 50 more stitches for the back; when you go to join for the round, place another different colored marker (or different kind) and then just start knitting. (yay, no purling in the round!) Knit for 12 inches (or whatever the pattern or however long you want to make it).
Then for the armhole shaping you'd switch to straight needles, knit the front and back separatly, then seam it at the sholder (or use a 3 needle bind off, which might be beater). Viola!
Did I answer your question? Sometimes I have trouble putting "what to do" into words....