Here you can find Maple code and worksheets for computing relative volumes, vertices, dimension, etc.. of type A and types B,C,D flow polytopes. This code uses Matthias Franz Maple convex package (you can download it here, look at the README file on how to install).
Requirements:
Maple 7 or later
Matthias Franz's Maple convex package
Setup:
save flowpolycode (text file with code) and volFlowPolytopes.mw (Maple worksheet) in the same folder
open worksheet volFlowPolytopes.mw and run the commands and the examples.