Bellow are a whole bunch of online resources I have found which helped me understand how flue pipes work and how to build them. Disclosure: There is allot of math involved.

 

http://en.wikipedia.org/wiki/Organ_flue_pipe_scaling

http://en.wikipedia.org/wiki/Flue_pipe

http://www.sci-experiments.com/organ_pipes/Organ_Pipes.html

http://www.instructables.com/id/Building-Your-Own-Homemade-Flue-Pipe/

http://ssngai-organs.blogspot.com/2011/06/cardboard-flue-pipe-schematic.html

http://www.pykett.org.uk/how_the_flue_pipe_speaks.htm

http://www.lawrencephelps.com/Documents/Articles/Beginner/pipeorgans101.html

http://www.theatreorgans.com/technical/

https://math.dartmouth.edu/archive/m5f11/public_html/proj/Griffith.pdf