From the December 2011 issue of Railroad Model Craftsman, this is a track car shed designed from plans used by the Duluth, Missabe & Northern Railway.
You can run a short piece of track perpendicular from the outside rail of your rail line into the track car shed as shown in the thumbnail picture. Put a hand car or track speeder in the shed for more realism.
It can also be used as yard, garden or pool shed to store appropriate tools.