Making one in the editor would come with a little line that can be edited to make a path. The drone follows the path, switching direction at the endpoint, possibly unless the first and last points intersect. It can be set to a team and can have auto-repair like a turret.
As for Engineering Drones? I don't know. Perhaps they can float to the nearest object and orbit it, or float in the direction the Engineer is facing bouncing off walls... I'm thinking Engineered Drones can be moved past freely.
Questions to be answered if this is implemented:
-Do Drones switch direction if the first and last points of their path are joined? (Wondering if this is hard to implement or not.)
-How will Engineered Drones work? (Bounce off walls? Orbit an object? Chase enemies down? Not engineerable in the first place?)
-Can turrets target drones?
-Can drones target turrets?
-Can drones stop to shoot at Forcefields?
-If a drone collides with a barrier, forcefield, etc. then does it keep moving like a moron in that direction or turn around and go the other way? Can drones move through forcefields of enemy teams?
-Is this ridiculously hard to implement?
Questions? Comments? Scathing rebukes?