Get your taxes done using TurboTax

You cannot base a Roth IRA contribution on earnings that are not taxable. IRS Publication 590-A says:

"If contributions are made only to Roth IRAs, your contribution limit is generally the lesser of:
• $7,000 ($8,000 if you are age 50 or older), or
• Your taxable compensation."

Since your taxable compensation is zero, the maximum that you can contribute to a Roth IRA is zero.