What you do might work. Where are you getting your geojson file? From Navigate? If from Navigate, just use the Navigate control that is part of the Map control to provide direction AND set the TransportationMethod to Walking. Depending on whether map tiles for your campus have sufficient detail of your campus buildings, that might work.
The Navigate control can display the path from one place to another and provide 'directions' which sometimes are right. 
Convert the geojson from Navigate to a List then use the first or last item to set your 'start' and 'finish' Markers. Navigate also can provide 'distance'.
An app that uses a different technique to find buildings and rooms on a campus is described here:
How to make a Custom Map Overlay Part II .. Show the user on the Map and a Custom Map Overlay The tutorial might help you add features to your app.