Rap songs are composed of rhyming couplets, called bars, as well as catchy choruses. In order to write your own chorus, you'll have to think of the lyrics that are suitable to the genre. Your hip-hop chorus can be about fast cars, inner city life, politics, or girls. Just keep in mind that it's like the glue that holds each verse together and it will repeat several times throughout the track.
Come up with an idea, phrase, or word that unifies each verse in the song. The chorus is often the most memorable portion of the song, so think about the message you want to send.
Write one line that encompasses the word, phrase or message that you've chosen. It can be as simple as "This is my life. This is my song."
Compose another line that rhymes with the first one. If the first line didn't, this line can contain the title of the song. For example, if you follow up with "Can do no right. Can do no wrong", you might title the song "Do No Wrong".