Put the AC into a diode and then through a resistor into a DC milliammeter. Draw the scale to read AC volts.
Look up the DC value of a half-wave AC waveform; it's about 50 V for 120 VRMS in but there is a PI in the formula somewhere.
50 µA full scale meter needs 50 V/50 µA = 1 MΩ resistor.
The diode PRV should be > 200 V; use 400.
Your meter will respond to the average [not the RMS] value of the AC waveform but you can put RMS on the meter face anyway. A lot of people do.
In the old days they just started the scale from the equivalent of 0.7V. No one except Clarke Kent noticed.
That reminds me of a comment made by the late Bob Monkhouse. He asked, why do people think I'm from Kent. When asked why he thought that he replied "when I walk past people I keep hearing them whispering Kent"!