How do I define roles and responsibilities for a project if it's similar to 3-4 projects I have worked on?
Should I keep repeating the same stuff or do something else to notify the employer that I performed similar role in variety of projects?
You can mention the aspect of common responsibilities in a section at the top that gives a summary of your resume. E.g. Performed project management, system architecture and design responsibilities across projects A, B and C.
In the actual experience section, focus on the unique experience and responsibilities for each project/job.