"The men build the house."
Translation:남자들이 집을 지어요.
As I understand it, it depends on if the word has a vowel or a consonant at the end. 집 ends with ㅂ which is a vowel, so the particle is 을 with the ㅇ "making space" for the consonant sound. If we were talking about a dog, 개 then the particle would be 를 because of the ㅐ at the end.