Hi Luis,
Mostly he writes the score on sheet music book, for this one I think he just composed whole tune with memory. Some of the other tunes he develops the idea on piano and writes half the score and does rest from memory. The current one he is creating again from memory i.e he created first verse yesterday and second one today and continue this next couple of days to complete. I have to tell something which I found interesting and observed couple of days ago, there is another tune he composed from memory and i recorded on Piano and asked him to change second half to reduce the time. He did that on newly installed Selebius software but it is completely different and not as good as when he creates music on the piano (the music sounded like when he created purely in ableton). I have asked him to create music on piano and write the score on software and he is doing that for the other tune he has done.