This is pdf sized for a 24 x 36 inch poster. Send this file to your local print company and laminate for a great visual in your science classroom. Search out local blueprint companies. My experience has been that they are able to print these large posters very cheap.
In my experience having more than three in a lab group can offer additional challenges. Keeping the roles simple and specific helps students and groups stay focused. Check out my store for Lab Role Circles to post on your board for student group assignments.