code: def make_roi(cls, sources=None):
          
          if sources is None:
              sources = {}
          src_fact = cls()
          src_fact.add_sources(sources)
          ret_model = roi_model.ROIModel(
              {}, skydir=SkyCoord(0.0, 0.0, unit='deg'))
          for source in src_fact.sources.values():
              ret_model.load_source(source,
                                    build_index=False, merge_sources=False)
          return ret_model
docs: Build and return a `fermipy.roi_model.ROIModel` object from
          a dict with information about the sources