I've made a few, they are easy, one thing I have noticed is that the piezo picks up EVERYTHING, from my fingers brushing the back side of the neck, to my daughter talking to me from a foot or two a way. It is SUPER easy to make, you might even get away with making one without soldering if you are sneaky. But as for me and mine, we will use the solder. I saw a video of a guy putting a pot on his piezo, and thats a sharp idea, that way you can cut back on the sound output at the uke. I am putting another one in a cheap soprano, I will try and video it, its pretty easy and straight forward stuff.....
buzzer@ the shack = $3
1/4" jack = $3 for 2
having your wife come out of the bed room at 1:30 in the morning saying, "seriously? turn it down." = priceless.
i play my small uke on a cigar box amp i built and its too fun......amp number 2 has vol gain and tone pots with a grit mode.. will fire that one up soon...