and here is the step by step guide: https://forum.audacityteam.org/t/building-audacity-2-3-0-on-ubuntu-16-0-4/50371/1
Official documentation may be found in these links:
https://github.com/audacity/audacity/blob/master/linux/build.txt
https://wiki.audacityteam.org/wiki/Building_On_Linux