Hi, see picture below. I increased the length of the tripod with 20 cm compared to my initial attempt using some pipe. The magnet foot works well on the car roof and is strong enough to carry the 100g camera. Will depend on the magnet ofcourse, and always try on a safe place before entering public roads.
Example 360 picture (magnet with only the tripod, not yet enlarged with pipe): https://www.mapillary.com/app/?lat=51.919047443426024&lng=4.5814299274936445&z=17&pKey=TtSBOI284l14p3Yr_cwMoA
-magnet foot from old speaker: free,
-tripod from cheap Dutch store 'Action' for 2 euro
-20 cm pipe found in my garage
-two component epoxy glue was most expensive 10 euro.