does anyone know what are the odds of having an eevee egg from a male eevee and a female rattata

anda can't. anda need the Eevee to be a female. Because in Pokemon breeding, the Hatched Pokemon is the Pokemon of the female. It takes the Moveset of the male Pokemon.
TL;DR ; anda need a Ditto instead of a Rattata. atau a Female Eevee

0.000000000000000000000000000000000000000001% Baically one unless anda get a funky glitch, thats the one at the end.The eevee must be a female atau breed with a ditto, like the person above me said.