Are you using the CLI or PhoneGap Build?
cloud build through build.phonegap.com
both ios and android are building fine. on windows target same error 'The OutputPath property is not set for project 'ZipWinProj.csproj''. it stopped working about 2 weeks ago. ??? not many people may need windows targets :-)
it looks like something changed in phonegap windows build environment.
We have also encountered this build error.
A temporary fix was for us to turn off hydration in PhoneGap build, though this is not ideal in the long term.
Is the PhoneGap Build team looking into this issue?
Further to this we have found that also including the preference "windows-appx-target" in the config.xml also fixes this issue e.g.
<preference name="windows-appx-target" value="8.1-phone" />