Go over your headings and consider overarching subjects. Also, consider how you would want to convey your found information to your readers.
The first step in producing an outline based on your findings is grouping quotes on the same or similar subjects. These overarching subjects will most likely be your top headings with more specific headings fitting under the top heading.
The next step in producing your outline based on your findings is collapsing the same or similar quote subject headings into one overarching heading that will, very likely, become your main headings.
The final step in producing an outline based on your findings is reorganizing the headers and quotations into a logical flow.