Sample Nant build file for use with MSBuild to package a Web Application. Some detail were found on Octopus Deploy around the OctoPack tool

WebApp.xml

<!-- This is from a Nant File with the following properties defined 

msbuild.target = Debug | Release
scratch.path = Path\for\some\temporary\folder\for\build\to\go\to
publish.path = Path\where\you\want\the\resulting\zip\or\package\to\end\up

Be sure the OutDir ends with a slash (escaped in this case) otherwise msbuild complains.
OutputPath must NOT have a trailing slash.

WebUI = This is just what I have in the sample, change it to whatever you want for the web ui stuff to go to. This is where your configs and Views will get put, then the bins under that.
-->

<msbuild project="THE-WEB-PROJECT-FOLDER\THE-WEB-PROJECT.csproj">
  <property name="Configuration" value="${msbuild.target}" readonly="true" />
	<property name="Platform" value="Any CPU" readonly="true" />
	<property name="WebProjectOutputDir" value="..\${scratch.path}\WebUI" />
	<property name="OutDir" value="..\${scratch.path}\WebUI\bin\\" /> 
	<property name="OutputPath" value="..\${scratch.path}\WebUI\bin" /> 
	<property name="Targets" value="ResolveReferences;_CopyWebApplication" /> 
</msbuild>

<zip zipfile="${publish.path}\THE-WEB-PROJECT.zip">
	<fileset basedir="${scratch.path}\WebUI">
		<include name="**/*" />
	</fileset>
</zip>