This is what I have done (several times):

1) Downloaded, extracted the files and initiated Umbraco 8 for the first time

2) Created datatypes, templates and content. Everything worked!

3) Found out that I needed to custom controllers

4) Changed the webconfig:
from: <add key="Umbraco.ModelsBuilder.ModelsMode" value="PureLive" />
to: <add key="Umbraco.ModelsBuilder.ModelsMode" value="AppData" />

5) Tried to rebuild the application..... Error!

6) Visual Studio 2019 was unable to compile Umbraco 8:
"The CodeDom provider type "Microsoft.VisualC.CppCodeProvider, CppCodeProvider, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" could not be located."

7) Changed the webconfig (back):
from: <add key="Umbraco.ModelsBuilder.ModelsMode" value="AppData" />
to: <add key="Umbraco.ModelsBuilder.ModelsMode" value="PureLive" />

8) Still unable to build and run Umbraco!

(On a Q/A someone wrote that the "CodeDom provider" was removed in Visual Studio > 2015)

• why do I get the error?
• what can I do to be able to build Umbraco 8 with my custom models and controllers?