I recently went through the exercise of getting the Armbian build system set up to create an image with some of my user customizations, similar to the example with OMV. The documentation and forums have been a huge help!
As I am running Fedora and Windows as my main OSes, I did struggle a bit at first. I tried, in order:
Ignoring the advice of the documentation, and running ./compile.sh on Fedora. Didn't get far
Running the build with Docker on Fedora. I ran into a number of different problems and ultimately gave up.
Running on Ubuntu 18.04 on WSL2. I did eventually get a build to complete, but the image may have been corrupt because my device didn't boot at all
Considered using Vagrant, but decided to give Multipass a try. Worked like a charm on the first try on both my environments!
I didn't find anything on the forums or documentation about using multipass to manage build VMs, so I decided to create a small gist here documenting how I got it working: https://gist.github.com/atomic77/7633fcdbf99dca80f31fd6d64bfd0565
For any not familiar, multipass is a Canonical tool that is optimized for creating Ubuntu VMs, which seems perfect for Armbian since that's the preferred platform anyway. Since it's so focused, it's very simple to use and all the utilities like shared mounts work seamlessly compared to Vagrant.
If this could be helpful to others, I'd be happy to incorporate any feedback into a page for the documentation.