If you want to build CE yourself, pick your platform and preferred build system and follow the instructions.
This is the build system used for the CI system on github. It does not execute arbitrary code from .csproj files, which makes it suitable for building PRs with repository secrets.
It requires python3.6 or later, wget, and mono (a recent enough version to have the Roslyn (csc) compiler).
You can get the full usage string via python3 Make.py --help.
If you want to use it to generate publicized assemblies (required starting with CE for RW 1.3), you need to check out the AssemblyPublicizer ( https://github.com/CombatExtended-Continued/AssemblyPublicizer )
and tell Make.py where to find it.
The invocation used by CI is about as simple as it gets.
python Make.py --all-libs --download-libs (for RW < 1.3), or
python Make.py --download-libs --all-libs --publicize Assembly-CSharp.dll,UnityEngine.CoreModule.dll --publicizer=$PWD/AssemblyPublicizer (for RW >= 1.3)
To install and open in either Rider or Visual Studio.
$ git clone https://github.com/CombatExtended-Continued/CombatExtended
$ start CombatExtended/Source/CombatExtended.sln
start will open the sln file with whatever IDE you have set to open .sln files by default. You can also just open the sln file normally.
After this, building is just building the solution, references will be pulled from Nuget, and the assemblies should be automatically publicised by the msbuild task. The resulting assembly will be in $(root)/Assemblies/CombatExtended.dll.
If you have a build system not listed here, please document how to use it.