It's fairly easy to add a simple collar to a neckline.  After sewing the shoulder seams, measure the length of the neck opening from center front to center front.  Cut a rectangle a couple of inches longer by 7" wide.  Interface one half (the facing) and baste that raw edge to the right side of the garment.  Turn the opposite raw edge under 1/2".  RST, sew the ends of the collar even with the center fronts and trim.  Turn and sew the folded edge over the seam.  This collar will not form lapels.