Learn Arabic (Modern Standard): شيد المقاولون مبنى جديدا. - The contractors constructed a new building.

In Arabic, when the verb comes before an explicit subject (making it a verbal sentence), the verb always stays in the singular form. Because شيد comes before المقاولون, it remains singular and only matches the masculine gender of the contractors.

Why does المقاولون end in ـون rather than ـين?

The word المقاولون is the subject doing the action of the verb, which means it is in the nominative case. For regular masculine plural nouns, the nominative case is marked by the ـون ending. If it were the object of the sentence or came after a preposition, it would change to ـين.

Why does the adjective جديدا have an extra alif at the end, but the noun it describes, مبنى, does not?

Both words are in the accusative case because they form the direct object of the verb. The adjective جديدا takes the standard accusative marker for indefinite nouns, which is an extra alif. However, the noun مبنى ends in an alif maqsurah (the letter ى). Nouns ending in this letter cannot take an extra alif for the accusative case, so their spelling remains the same.

What is the difference between شيد and the more common verb for building, بنى?