The main challenge you'll have with writing a WCF service is doing authentication. I'm not aware of a straightforward way to proxy authentication with your WCF service into the OneDrive service. The easiest approach would be to have the caller of the WCF service handle generating the auth token (see the examples for how to generate an auth token in the OAuth reference) and pass it to your service as one of the call parameters.
After that, you can use the Live SDK to make server-side calls using the token provided to your service from the caller as a parameter to your WCF method. You can either use the Live SDK to generate those calls, or you can make them yourself following the REST reference. Neither give you an object model that you can interact with, you'll need to understand how the REST service works and the structure of the returned JSON data to use the Live SDK.