This is just a draft, unfinished! Just some ideas. Unlikely to be ever finished. For special setups and advanced users only. Only in case the Download version, Other Operating Systems, Physical Isolation or Dev/Build Documentation instructions are not suitable, for example if you like to use another distribution as the base for Whonix-Gateway ™. Dev/Build Anonymity has not been considered.
This assumes Whonix ™ 7 or above.
Dev/Source Code Intro contains a source code introduction.
Look into Whonix ™ source code. It is mostly an installing and copy and paste task.
Look into the source file ./build-steps/45_create-vbox-vm. See function general_setup to see which commands are used to create both Virtual Machines, apply hardware_modifications on both machines, and also apply gateway_specific or workstation_specific accordingly.
After installing the operating system...
- Packages listed in /home/user/Whonix/development/Whonix-Gateway_packages have to be installed on Whonix-Gateway ™.
- Packages listed in /home/user/Whonix/development/Whonix-Workstation_packages have to be installed on Whonix-Workstation ™.
All files within whonix_gateway folder are configuration files supposed to be installed on Whonix-Gateway ™. For example /home/user/Whonix/whonix_gateway/usr/local/etc/torrc.d/50_user.conf is supposed to be installed on Whonix-Gateway ™ under /usr/local/etc/torrc.d/50_user.conf.
All files within whonix_workstation folder are configuration files supposed to be installed on Whonix-Workstation ™. For example /home/user/Whonix/whonix_workstation/usr/local/bin/xchat-reset is supposed to be copied to /usr/local/bin/xchat-reset on Whonix-Workstation ™.
whonix_shared are configuration files supposed to be installed on Whonix-Gateway ™ and Whonix-Workstation ™. For example /home/user/Whonix/whonix_shared/etc/sudoers.d/whonix is supposed to be copied to /etc/sudoers.d/whonix on Whonix-Gateway ™ and Whonix-Workstation ™.
You don't have to bother with most other files in Whonix ™ source folder.  Just read README and LICENSE.
- /whonix_gateway/usr/share/whonix/chroot-scripts-pre.d are run inside Whonix-Gateway ™
- /whonix_workstation/usr/share/whonix/chroot-scripts-pre.d are run inside Whonix-Workstation ™
- /whonix_shared/usr/share/whonix/chroot-scripts-pre.d are run inside Whonix-Gateway ™ and Whonix-Workstation ™
- There are also chroot-scripts-post.d folders.
You can also read the scripts and only run the commands you find sensible manually one by one.
- Those are used for image creation and Virtual Machine creation.