Actually, one of the easiest things in the world is to build Godot from the source.
All you have to do is:
1. Download the dependencies
- Visual Studio Community, version 2017 or later. VS 2019 is recommended.
- MinGW-w64 with GCC can be used as an alternative to Visual Studio.
- Python 3.5+.
- SCons 3.0 build system. If using Visual Studio 2019, you need at least SCons 3.1.1.
- Optional - yasm (for WebM SIMD optimizations)
2. Download the master-branch of the Godot sourcecode
https://github.com/godotengine/godot
3. In the Godot folder, execute the command "scons".
I also made a whole series of videos about how you can program entire games only in C++ directly in the source code.
I can only recommend a look at :)
Regards
ProggerParrot