What is this type of job called?

OKay, well im a Techi Person for Drama which means that i build the stage and work the lights and all that stuff for the actors and airband. well, today when me and the other Techs went to the Auditorium to finish building the stage there was some people they weren't Teachers or anyone who works at the skool, the skool had hired them to Build the things and kind of like all that stuff that goes up in the stage that hold up the lights, Im not really sure what they are called so i found this picture --->a href="http://en.wikipedia.org/wiki/File:Stage_on_stage.JPG" rel="nofollow"http://en.wikipedia.org/wiki/File:Stage_…/a there all those Metal parts that look kinda of like ladders around the stage, thts what they where bulilding, So we dieceded to bulid up a conversation since The Mrs. was at the Choir room w/ the actors and me and like 5 other Techs were w/ this People building the bottom part of the stage, while they were bulilding the top. So, we asked them how much they made an year by doing this and they said 100,000,000 an year. Then one of the Techs asked them if they have every built one for a Concert of Avengend SevenFold and they said Yeah and they got to see them and that they were really rude and had a big Ego. and they said they built the stage for alot of Famous ppls concerts already that they have lost track. So i wana know wat are the name of the job these ppl have, they also told us they worked for a Company i just cant remember the name??