'no da' is legal, sort of throwing the whole sentence around as one big noun phrase, like,
Hi ga aru. "There's a fire"
Hi ga aru n(o) da. "The fact that there is a fire, exists."
You usually see it either dialectically or more in polite speech (as "n(o) desu"), like
Boku wa mizu ga hoshii n desu ga. "I'd like some water [please]"
comes out more polite than
Boku wa mizu ga hoshii desu. "I'd like some water"
or, not being a native speaker, "so I am told"
"you're a doctor.... and 27 years.... so...doctor + 27 years = HATORI SOHMA" - RoyalWing, when I was 27
"Al hail the forum editting Shooby! His vibes are law!" - Osaka-chan
I could still be champ, but I'd feel bad taking it away from one of the younger guys. - George Foreman