This is an easy project!
Grab some festive knit fabric, your basic upper body block, and a sewing machine!
Trace your basic body block on construction paper (or poser board). Then slash the neck, armholes, and hem to your desired shape/style (red dotted lines in illustration). Then cut out your new body block pattern.
Slash your pattern (black dotted lines in the illustration).
After you slash your pattern, trace the new pattern pieces (adding your seam allowance).
Cut fabric using your new pattern pieces and SEW!