Great question — answering as the UphillTech team:
I think your best bet will be to befriend locals. As it is not easy to meet the right people by accident, you can try the online meeting places. I would personally start with any members of any groups I am already part of who happen to live in Paris, but that depends on being part of an international or French organization. If you are not (yet) you may look if your hobby has regional or local groups with online presence, as you will have your hobby to talk about (rather than just begging access to their roofs.) Next are the sites that are specially made for meeting people, couch surfing among others, and sites where people who travel hang out, (I am told the Lonely Planet site has one that...
Full answer by Willeke: https://travel.stackexchange.com/a/156871 (CC BY-SA 4.0).
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