Well it is very difficult to find some information about
the game engine. The best resources in my opinion are the github
repositories, general tutorials of ROM hacking
and the Pokémon ROM.
Maybe you can ask some people of this forum, if you
have a special problem, but the most time you have to
work on your own.
On this forum is one tutorial about a make file project:
Do you need english resources or can you work with german resources too?