There are many methods available to make your own Ukulele strap. The method illustrated in This Video is not one I would recommend.
Using string as a Ukulele strap probably would work. The Uke doesn’t weigh that much after all. And I’ve seen people using shoe laces as straps. But Scotch-taping the string to the back of your Uke to hold it from slipping is just a bit too much for my taste. And wrapping the string around the entire body of the Uke probably is not such a good idea.
If you need a strap for your Uke, just go out and buy yourself a Uke Leash.
Just don’t Scotch Tape it to the back of your Uke.