Sorry for the huge delay in getting the next Build a Seam stitch out. My new job and a heavy teaching schedule this month are really playing havoc with my time! Excuse my less than perfect first attempt at this stitch and have fun creating it yourself!
Start by bringing your needle up at the left hand side and take it down again directly across on the far side of the seam. Bring your needle back up again in the center. You can get different effects by either making your center stitch a bit lower as I have which creates a slanted chevron effect or you can make your center stitch parallel to the long stitch instead.
Roman Stitch is good for use in leaf shapes as well as other forms where you might want a center rib effect. Have fun with it!