I can't recall seeing the crows group up and fly to a roost in the summer however in fall/winter this is quite common and I know there is a flyway that goes from downtown north past Mt. Doug, sometimes on the east side, sometimes on the west. Best viewing was Christmas Hill, Mt. Doug, and best time in the fall was around 4-5pm I think. In winter, more like 3pm.
I am not sure where the crow roost is now but possible they are on still on Darcy Is. or somewhere around Gordon Head/Cormorant Pt.