The base is original from the producer (chords and melodies), but is complemented with elements that complement the song that come from samplepacks, usually, vocal chops, guitars, wobbles sections, glitch effects. It is the standard in which most of producers work, in a project you will find MIDI files made by the producer, but also melodic loops.
Process note
I used royalty free guitar sample from pack, FXed it and changed for perfect sit in the track.
Basses - Vital, Serum; Pads - Spire, Absynth 5; Chords - Serum, Spire; Pianos - Addictive Keys; Plucks - Spire; Drop leads - Vital; Choir - Nexus.
Melodic loops
Instrument Guitar
Sample pack Savage Sounds - ENGINE 2.0
Loop name Savage Sounds - ENGINE 2.0 - Guitar Riff 02 - C#min