"I would begin with a review of the scope of the user story. The team would discuss any assumptions regarding the basic definition of completion and any must-have user expectations or business rules that need to be considered.
From there, I would allow everyone on the team to offer their estimate. The estimates given are not specific to each role. They are estimates for the total size of the user story. Additionally, the estimates are not given in terms of hours or days. They are relative estimates that are made by comparing the size of the new story, to other upcoming stories, or to similar stories that have been completed in the past. The teams I work with use a Fibonacci scale of 1, 2, 3, 5, 8, and 13. Anything above a 13 typically needs to be decomposed into smaller jobs.
After everyone provides their number, we discuss any sizing disagreements. The parties who disagree offer the logic behind their estimate and the team determines how to proceed. If there is a deadlock, we defer to the individual who is most likely to do the work for the story and go with their estimate."
