In order to automatically construct your nuget packages you can use OctoPack. Octopack allows you to specify a .nuspec file which will be used to specify how your .nupkg should be created.

Follow the core instructions for creating your .nuspec file on the OctoPack page.

You'll then need to add a files specification to match Squirrel's expected .nupkg structure:

  <files>
    <file src="bin\Release\*.*" target="lib\net45\" exclude="bin\release\*.pdb;bin\release\*.nupkg;bin\release\*.vshost.*"/>
  </files>

If you're building using Visual Studio, you will also need to edit your .csproj file to include a property group.

  <PropertyGroup>
    <RunOctoPack>true</RunOctoPack>
  </PropertyGroup>

If you're using a build server, see OctoPack's guides on how to trigger it to be run.