I've struggled to get my head around Robomaker and still have not gotten even a simple robotic example to work. Have you located any documentation that is more complete than one Amazon offers?
I'm a product manager from the AWS RoboMaker team. We have a tutorial that can help you get started with the service: Projects on AWS: How to Train a Robot Using Reinforcement Learning with AWS RoboMaker
If you have any questions or feedback for the service, please reach out to me and I would love to help and take your feedback to improve our service.