How do you convert 12V to 110AC?

Is the 12V AC or DC?

If it's AC, you find a transformer that can step up voltage by approximately a factor of 10, and adjust the output as necessary (e.g. with a voltage divider).

If it's DC, then you can build an oscillator that runs on 12V DC and then put it into a transformer. Be sure to know how your oscillator's waveform is effected by the transformer.