Runs a Windows batch script for building the project. The script will be run with the workspace as the current directory. The text you enter in the text box will be executed as a batch file, and a build will be considered a failure if at the end of the execution %ERRORLEVEL% is not 0.

If you already have a batch file in SCM, you can just type in the path of that batch file (again relative to the workspace directory), and simply execute that.