return collections of complex types

what is best practice on returning collections of complex types.

In my case I would like to return collections of items, that contain additional custom metadata of existing objects.

Is there an inheritance model I can use to extend existing objects, or do I need to create a wrapper and migrate content into the wrapper object.

For example lets assume I have a vApp with a collection of VirtualMachines. However each machine has custom attributes stored somewhere.

VApp

     Machine1

          CustomAttribute1

          CustomAttribute2

     Machine2

          CustomAttribute1

          CustomAttribute2

     Machine3    

          CustomAttribute1

          CustomAttribute2

Can I simply extend the existing models somehow to allow a third party to consume that model? Or do I need to create a new Collection of .props objects for example?

How does everyone else handle this type of information? I know there is numerous ways to do this but curious if anyone has come up with some good clean examples / ideas.

Regards,

John