For this cardi, I used a ready-to-wear, long-sleeved jersey cardigan as a pattern. I didn't cut it apart. I just folded each section in half, laid it on my fabric, and added a seam allowance while cutting. It is just one back, cut on the fold, two fronts, and two sleeves. The only tricky part was getting the back neck collar area (attached to the fronts) just right. I just laid it out as flat as I could and it turned out fine.
I can't tell you how to go forth and make this for yourself because I didn't use a pattern, but maybe it will inspire you to look through your closet for a simple garment you love that you can easily reproduce without even taking it apart!