Questions & Answers about Мы строим дом, нам очень нужны гвозди.
Why do we use нужны here instead of the default нужно?
In this construction, the word for need (нужен) is actually a short adjective that agrees with the thing being needed. Since гвозди (nails) is plural, we use the plural form нужны. If we needed a singular masculine noun, it would be нужен.
Why does the second part of the sentence start with нам instead of мы?
In Russian, you do not directly say we need nails. Instead, the literal structure is to us, nails are necessary. The person who needs something must be in the Dative case, so мы (we) becomes нам (to us).
What case is гвозди in here?
It is in the Nominative case. Because the literal translation of the construction is nails are necessary to us, гвозди is the grammatical subject of the second clause.
What is the singular form of гвозди and what gender is it?
The singular is гвоздь (a nail). Even though it ends in a soft sign (-ь), it is a masculine noun. Its plural is formed by changing the soft sign to -и, giving us гвозди.
Why does строим take an -им ending?