How do I extrude ledges evenly on my villa model? I'm trying to create ledges at the top of my building to come out in steps. I'm using loop cuts and the extruding out along the normals. 


The problem is that the extrusion doesn't come out evenly - at certain points the edges are coming out more than on the corners. 


The object is properly scaled in object mode, which I understand can be the problem sometimes. Using 'individual origins' for the pivot point doesn't make any difference. Nothing else I've tried works, any help is greatly appreciated.
Enable the Offset Even option in the Last Operation box: