Estas preguntas subrayan la diferencia entre SER y ESTAR. Para repasar estos verbos, mira
Lesson 32: Usos de ser y estar / Uses of ser and estar
También hay un video en el Video Library donde yo explico la diferencia en términos básicos: Ser o Estar.
Note about events: To tell where an event takes place you must use SER. An event is any gathering or activity that could be scheduled (meeting, concert, game, etc.). In the sample sentence in the Yepes Manual, he uses "The class is in another building". This is probably not the best example as the English wording could be taken different ways. It's understood here that we mean "The class meeting is in another building." If we meant "The classroom is in another building" or "The group of people (being called the 'class') is in another building" then we would use ESTAR.