Condition to allow only if the user in specified field is in the specified role.
To add Check user in specified field is in specified role condition, go to the transition of your workflow, switch to Conditions tab and click on Add Condition button.
Select JEP - Check User In Specified Field Is In Specified Role Condition and click Add button
Select user field/custom field and the project role. Then click Add button
That's it, the condition is added to the transition.
Please do not forget to publish the workflow.