Just downloaded v1.6 source zip, then trying to run build.cmd from VS10 CMD, got error
"error MSB4019: The imported project "C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v11.0\WebApplications\Microsoft.WebApplication.targets" was not found."
And I don't have VS2012 on my machine. Had a look of .csproj, seems alright by setting <VisualStudioVersion> to 10.0. Finally found that the Orchard.sln is a VS2012 format file, thus why 10.0 was replaced by 11.0 in the run.
Not sure why we have a VS2012 sln file there, but in the meantime, calling msbuild by this in VS10 CMD will work:
msbuild /t:Build Orchard.proj /p:VisualStudioVersion=10.0