How to debug Team Build Project Files (TFSBuild.prj)
You can find it in the team build targets file, but no one seems to tell you, so I will. Run the team build project file locally on your box (using MSBuild) with the IsDesktopBuild property set to true:
C:\MyTeamProjectFolder\TeamBuildTypes\MyTeamBuildType>MSBuild TFSBuild.proj /p:IsDesktopBuild=true /v:diag > msbuild.log