code: def create_build_system(working_dir, buildsys_type=None, package=None, opts=None,
                          write_build_scripts=False, verbose=False,
                          build_args=[], child_build_args=[]):
      
      from rez.plugin_managers import plugin_manager
  
      # detect build system if necessary
      if not buildsys_type:
          clss = get_valid_build_systems(working_dir, package=package)
  
          if not clss:
              raise BuildSystemError(
                  "No build system is associated with the path %s" % working_dir)
  
          if len(clss) != 1:
              s = ', '.join(x.name() for x in clss)
              raise BuildSystemError(("Source could be built with one of: %s; "
                                     "Please specify a build system") % s)
  
          buildsys_type = iter(clss).next().name()
  
      # create instance of build system
      cls_ = plugin_manager.get_plugin_class('build_system', buildsys_type)
  
      return cls_(working_dir,
                  opts=opts,
                  package=package,
                  write_build_scripts=write_build_scripts,
                  verbose=verbose,
                  build_args=build_args,
                  child_build_args=child_build_args)
docs: Return a new build system that can build the source in working_dir.