I'm aware that neon sign transformers (NSTs?) produce high voltage - up to 15kv. But I cannot picture what's inside of one. Wikipedia seems to indicate that they may be a form of resonant transformer but provides no diagram. Googling "resonant transformer" shows images that may be laminated core or toroidal based, close proximity series transformers, but it's hard to tell.
What would a typical NST look like if it was cut open, and would it be possible (not that I want to try) for someone to home-build a HV transformer like a NST?
Note: I'd never trust myself to build one, so that may answer the second part of the question - if I wanted a tesla coil, I'd buy a working NST