For setpos all you need is this
This setpos[getpos this select 0, getpos this select 1, 4]
Works the same as decribed above, 4 is meters off the ground.
Also, if this is a non editor added building, EI, came with teh island in question, you can also simply make a waypoint on the building for the unit, and a new option becomes availeble, it shows up as position. and you select from several numbers, trial and error is about the only way to use it though until you find the right location in the building.
1st method would be used if you wanted him to start in teh building from the begining of the mission.
2nd would be for if you wanted him to move into it after it started.