Flys how do i armor class them

What do I use for a fly's armor class. I think it should be high because it is fast, but it is not tough itself. pls help.

Look up a Giant Fly, a monster that can be created by a figure of wondrous power

Mongo dex bonus and 1 Hp.  That's what I figure.

Probably around 27 DEX (18 AC) and can dodge as a bonus action.

High AC, 1 HP, can dodge.  18 does not seem at all unreasonable. Could go higher if you want, especially for in flight.

I sense a web spell in your near future! LOL

Or a monk proficient in chop sticks.