How to add new profiles to valhalla?

I try to add a new profile for firetrucks, which I derived from truck. Therefore I got the files
firetruckcost.h (derived from truckcost.h) and firetruckcost.cc (derived from truckcost.cc). Moreover I copied in graph.lua all statements which includes truck and renamed them to firetruck.

I tested it, but as expected it didn't work. I know there are a few other files for truck costs like libvalhalla_la-truckcost.lo, libvalhalla_la-truckcost.o, libvalhalla_la-truckcost.Plo. But I haven't got a clue how to create these. Also I don't know whether this is enough or not.

What do I have to change/ add exactly if want to create a new profile, in the documentation I only found that it is possible