If a person has net earnings over $400 from self-employment, they are required to file a federal income tax return.
Yes, they will likely be required to pay self-employment taxes. A Roth does not reduce your taxable earnings.
But what your doing is a great idea in building for the future. I encourage my son's to contribute to a Roth (even do a bit of matching).
https://www.irs.gov/individuals/self-employed
