Different genres of songs are constructed in different ways. Hip hop and rap songs are basically vocals on compilation of bass sounds and beats. Hip hop instrumentals usually have just two phases the phase for the chorus and the phase for the verses. Rap music is the same and so is R&B. in fact most music instrumentals are constructed that way. You do how ever have some genres of music that constructing an instrumental for is terribly annoying work, it will get you frustrated.