You've never seen a giant Tesla coil in operation have you? Believe me when you do you'll understand that you can absolutely not put such things into a public space like a science fair. They are very scary and definitely lethal.
I was able to cause a 4' long fluorescent bulb to light up at 15 feet away. And destroyed TV & radio reception for the neighbors while it was running. Being a big fan of Nikola Tesla at the time, my experiment was measuring the wireless delivery of power using an AC voltmeter at various distances. But mostly I built it because it was cool.
I used a 15kv neon sign transformer. The capacitor was made from two copper sheets glued to opposite sides of some picture frame glass, which was epoxied into a wooden frame (no metal fasteners allowed!). The spark gap was two threaded rods on a plastic frame so that I could adjust the frequency. The primary coil was bulk sparkplug wire. The secondary was two spools of magnet wire laid down on a 6" diameter PVC drain pipe, with several coats of lacquer sprayed over it (that gave me pneumonia from the fumes). I went through about 3 capacitors before I got a good one because the glass would crack in the family oven when I cured the epoxy.
>mostly I built it because it was cool.
I would say build it because you want it, then it'll be a science fair every time you run it.
In 6th grade we built one on a portable cart which was brought into class on project days until it was complete.
Ended up with a 6 foot tall coil topped with a classic copper flush toilet float. It would throw sparks a few feet to the closest fluorescent tube a kid was holding up.
Or simply put it inside metal wire cage and don't let people run it when you're not around.
There was also the building height Jacob's ladder over by the PC system builders section.
The lightning show (with Tesla coils) is absolutely wonderful.
A fun tidbit about the giant Van de Graaff generators they have was that they were built by Robert Van De Graaff himself as part of early linear particle accelerator experiments.
The public space aspect is also a "you need to stand back this far"
Note the suit that the person is wearing in the Derezzed video - https://youtu.be/psoLXEBmfRg
Also note the grounding fences around the area.
The video with them and Tested gets into the tech of it - https://youtu.be/4m6EjnEYEEg
Small one... ok. Big one? Nope.