An interesting Rube Goldberg approach, but frankly I suspect not a good one.
What happens with any kayak hull as you move them over a flat surface is that, since the hull is to some degree rounded, the boat tends to want to roll to one side or the other. When that happens as you move it while holding on no problem, you just counter it as you move it.
But if that happens while the boat is in the air a couple feet or more away from you is that it rolls over enough to come down off the roof. Possibly taking a side view mirror with it. This is a thought that occurs to me at 5â4", it may not jump out so quickly to someone several inches taller.
It is just not that hard. Start out with a boat that is long enough to reach from the ground to a support for the roof and that preferably has deck line (not bungie). Prop the bow of the boat onto the access point for the roof, taking advantage of the deck line and cockpit to control it. Grab the stern, lift and slide it on up rest of the way. Then make final adjustments and strap it down.
Note that this way you are never lifting the entire weight of the boat, I have a good cart to get it to and from the car.
Granted this is all easier with a third party rack, at least the cross bars. But your back matters too, so spend the money.
The prop I am talking about can be something like the Amagasett Roller Loader, wheels that hook onto the back of a car and can hold the boat, or a bar that sticks out sideways from a cross bar further than its normal length. Yakima had one at some point or people have made their own. Thule I think it is has a fancier version with an assembly that slides out back from the rear cross bar and you just slide the boat up on that.
It is advisable that what you strap the boat to is something that doesnât fight back when you are making the final position adjustments. The stackers were always easy with that, and in my current setup I went to glide pads in back on the non-Hullivator side because I found having saddle in back as well as front made the boat stick some when I was making the final adjustments. The glide pads solved that issue.
Above is why you hear that a longer boat is often easier than a 10 footer. In fact we had that experience with our evening paddle group. Women who had gotten the basic 10 footers often found it harder to cartop them alone than those of us with longer boats. Between the short length and the lack of deck rigging, they had to life the entire weight.