-n switch is not strictly a part of the
Build program. Instead, it is just passed to the
make(1) program, and the
Build program creates the
obj directory (if it doesn't
exist), and then populates it with a Makefile
and symbolic links. After that, Build invokes
make with the -n switch,
which only causes make to print what it would
do. It doesn't cause make to
actually do anything.
This -n switch is especially useful with the
install target, to preview what steps will be
undertaken to install the program before actually installing it.