What is motivation role in team building?

The function of team building is to turn a group of people into a team.  If this is done well, the team will be well motivated to do the job it was built for.

If the group of people are not motivated to become a team, it can be difficult to motivate them.  Simple, human techniques are often successful.  (E.g. "Who wants to go home early?  OK, as soon as everybody has done this and everybody has done that, we can all leave." )  This is much easier in a business environment than it is in general, because you have the carrot of pay and the stick of firing them.