I've put online my long article on how to write and arrange effective
music rolls for player piano.  It also includes a few musical examples
you can hear via MIDI whilst examining the perforation pattern on-screen.
Also you can just download and examine the examples in Cakewalk, etc.

For a very long time I have been puzzled as to why in the mechanical
organ world there are dozens of people constantly trying their hand at
roll or book arranging, whereas in the world of the player piano, where
there are a thousand-fold more instruments available, the number of 
active music arrangers never seems to exceed the fingers of one hand.

Granted, it is easier to get good results from an organ than from a
piano, and the financial incentive is greater.  Yet, the piano keyboard
still offers many unexplored musical possibilities, both for re-arranging
existing music and also for writing new music.

My article can be seen here:
     http://www.undergroundpianola.com/pianolacomposition.html 

This is not about MIDI files.  It is about creating new music for the
player piano.  It doesn't matter what tool you use to draw your next
music roll master.  I just happen to use MIDI-based software instead of
a cardboard 3-to-1 grid and a pencil.  From the on-screen pattern which
I create via MIDI, we create the virtual 3-to-1 master roll for the
electronically-signaled perforator, and the finished product has
chaining, themodist, etc.

If you get enthused and need a hand anytime, just drop me a line and/or
the MIDI file you are working on, and I'll be happy to discuss it and
help in any way I can.

Adam Ramet
www.undergroundpianola.com