tossen u failed to specify your level however am a grad of Q/S
example of building elements are doors, windows, foundation, wall roofing.(they are component that makes up a building) thats why in BOQs u will have element nr.1 as foundation, element nr 2 as blockwall etc
example of building trades are masonry iron mongery, bricklaying tiling renderingetc (80% sure please)
mail me to know how far
fundave4real@yahoo.com. wishing u success