base_dir statement is deprecated.
It persists to support tests which want to place their generated output in out of the way places for clutter reduction and easier cleanup.
If you do use it, it will only affect initial generation with -c. Then it specifies the parent of the build directory. By default that is the current directory.
base_dir must already exist.
To also control the name of the build dir,
use the deprecated
app_dir (but please don't).
To see an example, build:
bigtop -c example.bigtop all
Note that the build directory is called
useless_dir instead of