In this scenario, Roger's behaviour would best be classified as an elaborator.
While working in a group each individual contributes in their own ways.
Benne and Sheats defined roles in a group and classified them in three categories. These categories are
1. Task roles : relate to actually achieving the task goals.
2. Personal Roles : relate to the interpersonal relationships between team members. A highly qualified team, when all team members with a high ego will not be able to achieve the desired goal within the deadline.
3.Dysfunctional Roles: do not contribute in any way to a group. They are only interested in serving their own interests and more often than not, are responsible for disruptions and discord within the group.
The right combination of various roles in a group goes a long way in achieving a goal.
The Elaborator is a task role. The Elaborator takes up an idea and gives his views on how that idea might turn out if it is implemented in the given suggestion.