This guys does it pretty well.
https://youtu.be/s7gQKKBV648
Depending on the kayak determines weather it’s upside down or not. Hobies I load right side up since the bottoms are flat and most have rails and other stuff on top. Most of the paddle kayaks I’ve hade have a V hull and flat tops so they went upside down.
When securing it don’t over tighten the straps going across the kayak, they just need to be tight enough to keep it from sliding back and forth or raddling in the wind. The ropes going from the bumpers to the kayak are what keep it on the roof and should be taunt but not enough to flex the kayak.
Also, put a twist in any flat lines, like ratchet straps, otherwise they become a reed instrument and hum really loud at freeway speeds