The standard or itemized deduction has nothing to do with being able contribute to a Roth and if your income is low then why can't you contribute to a Roth?
You must have at least as much taxable compensation as the contribution.
The most you can contribute to all of your traditional and Roth IRAs is the smaller of:
For 2019, $6,000, or $7,000 if you’re age 50 or older by the end of the year; or
your taxable compensation for the year.
(Taxable compensation is generally wages that you worked for - W-2 or net self-employed income minus the deducible part of the SE tax, but can include commissions, certain alimony and separate maintenance, and nontaxable combat pay ).
See IRS Pub 590A "What is compensation" for details:
See this IRS article for Roth contribution limits: