There's also a very nice little book, "Railways and War before 1918" by Davis and Bishop (can be found at Amazon). Of 1970s vintage, it chronicles the use and various types of hardware of military railroading, illustrated in colour plates. A strong focus on Allied material, but some Central Powers types are featured as well. Much recommended.
Regarding actual modelling, former user is quite right - the possibly best option would be to get some cheap 00 or H0 gauge tracks plus matching wheelsets and scratchbuild from there.