A "village" is pretty explicitly small, so a "big village" sounds a bit strange.

In any case, Swahili has words that reflect three different sizes of urban areas. The translations I'm giving here are approximate:

kijiji / vijiji "village"
mji / miji "town"
jiji / majiji "city"

So, "big village", forgetting for a moment that it doesn't really make much sense (see below) would probably be kijiji kikubwa.

I guess you could say "big village" to describe a town or a city that has the feel or characteristics of a village (everyone knows everyone, etc.), but I really don't know if that would be idiomatic in Swahili.