This repository provide ready to use Vagrant boxes. You can download them from "releases" tab.
They are based on Ubuntu/amd64 server iso file and created using this script.
You can check:
- what parameters are used for unattended installation here
- what parameters are used to create VM Box here
- what is done after all here
As you can see, this is very minimalistic version and you can use it as a base, for your future modification with e.i. this Ansible roles.