So it may be different over there but this is how a few down here have been done in rough terms.
Have been in contact with a few who are currently in the process of getting a track started.
Main things to figure out are, where it will be put and how it will be funded, built and maintained.
Its all good to say "oh we have dirt, and a paddock over there" but it would need to be all approved by the appropriate channels.
To put it in perspective, we cannot even just get dirt without soil testing and the likes.
so here is a rough checklist
-Council Approved Land with all the paperwork that goes with it.
-it is likely this will require there to be a club association to go along with it (which thats a seperate issue all together)
-Funding for the facility.
-Cost to build the track
-Ancillary equipment such as the Gate, Concrete for the hill (maybe even corners), Tooling etc.
-Amenities for said facility (public access or not)
-Insurance stuff. so Public Liability for the club or the council insurance if it is public access.
Ways you can promote it are by showing there is interest and how it can help the community. Parents love scheduled commitments or planned events that their kids can go to. Maybe even try incorporate it with a skatepark next door and have a whole facility for Bikes/Scooters/Skateboards to promote a community atmosphere.
There is a track being built pretty close to us, its roughly a 2 year process so those who want to get involved should be happy to stay the course.
Its alot of work, but it does eventually get there.