A Tesla Coil is a high voltage device capable of producing millions of volts of high frequency AC current.
There is practically no limit to the size that it can be built, but like many things, it just becomes more expensive to make the larger it gets.
The image above is an 8 foot tall coil we recently built, and you can see from the
additional images below, that they can be built in a variety of configurations & sizes.

Photo courtesy of Ed Wingate