"Are we big?"

Translation: Sommes-nous gros ?

[Ghodsi]

Is it better to say "Sommes-nous grands?" or "Sommes-nous gros?"

[Sitesurf]

"grands" would be tall.

[Andypbt]

If "nous" referred to a group of females, would it be grosses?

[Sitesurf]

yes it would.

[totoyalove]

why is it sommes-nous? would you be able to say nous sommes gros? with the same meaning?

[Sitesurf]

That is the formal way of asking questions in French with inversion Verb-Subject pronoun.

Alternatively, the standard way uses an interrogative (invariable) formula: "est-ce que nous sommes gros ?".

At last, the oral/relaxed form is : "nous sommes gros ?"