msbuild.exe location on windows 8 with VS2012

The correct way to locate MSBuild is to use the registry.

Here's a powershell implementation of finding a specific version of the .exe

$regKey = "HKLM:\SOFTWARE\Microsoft\MSBuild\ToolsVersions\${Version}"
$itemProperty = Get-ItemProperty $RegKey -ErrorAction SilentlyContinue
if ($itemProperty -ne $null -and $itemProperty.MSBuildToolsPath -ne $null)
{
     $msBuildPath = Join-Path $itemProperty.MSBuildToolsPath -ChildPath "MsBuild.exe"
}

Make sure that you have installed the corresponding .Net framework. You can find the build.exe by following this sample path

C:\Windows\Microsoft.NET\Framework\v4.5\MSBuild.exe