Generally speaking, you are not prohibited from making a Roth IRA contribution because of contributing to a SEP-IRA. The SEP-IRA contribution limits are independent of the combined traditional and Roth IRA limit of $5500 (plus $1000 if age 50 or over).
However, contributing to a SEP-IRA does lower the amount of your Adjusted Gross Income, so the change in AGI can affect your eligibility to contribute to the Roth IRA (usually increasing your eligibility).
