Sometimes you want to move a unit to another floor in a building or more often or not you want to pile sandbags on top of each other to provide more cover.
unitA setpos [getpos unitA select 0, getpos unitA select 1, (getpos unitA select 2) + 5]
That will place unitA, 5 metres in the air at his current position. When placing units within buildings, height values need to be experimented with.