Coding is surprisingly easy, you just need to get started.
The basic principle of coding is to choose an existing vehicle to modify, then change its name, statistics and graphics - you cannot add vehicles, only replace them. Start with this tutorial (
http://wiki.ttdpatch.net/tiki-index.php ... oundations) and try to modify the graphics of a train to your graphics. The basic sample nfo file (
http://wiki.ttdpatch.net/tiki-index.php ... pleNfoFile) may also be useful.
For a basic grf with a single train you will eventually need:
Grfcodec header
Number of sprites in the file
Action 8: Describes the grf, with grfid, name and description.
Action 4: Changes vehicle names.
Action 0: Changes vehicle statistics.
Action 1, real sprites, Action 2s and Action 3: Defines new graphics and their usage.
To code the carriages to match the engine you will need an Action 3 livery override (
http://wiki.ttdpatch.net/tiki-index.php ... 20override), but first try to make a basic grf without using this.
I am very happy to walk you through any stages you get stuck at, but it is far better to try on your own to start, you pick it up much faster!