Creating routing file

Ive been playing around with the offline android router
It’s fantastic.
I would now like to swap out the monaco files and insert files for New Zealand which as far as I can tell are not catered for in the demo.
I see OSM have some prebuilt files but of course I need to make the routing file too. I assume I need both a .map file and the routing file , Do I need to do this on a java server or is there another method ?
Also while I’m here : thanks, this is an amazing library and very important for the open source mapping ecosystem