Districts are not required to offer a Roth 403(b) or Roth 457, but many are offering them or plan to add them. You cannot invest in a Roth 403(b) or Roth 457 on your own – these types of plans are available only through your employer. If your district does not currently offer a Roth option, you may want to contact your district directly or check with your chapter president to encourage the district to do so.
You can invest in a Roth individual retirement account (IRA) on your own if you wish. However, contributions limits are much lower and eligibility is limited by income. Read more about Roth IRAs here.