99% of film cues are mocked up by the composer or a member of their team. This means there is a version of the cue done with samples and synths inside a computer. Some of these are very fancy and complete, while others have just enough information to show the director what the orchestra might sound like.
These mockups, along with the MIDI file of the sequence, are what are sent to the orchestrator to work from. John Williams is the only person that works on big movies and still writes a pencil sketch for his orchestrator. There are others that do pencil sketching, but it will be mocked up at some stage.