Coming into Coventry on the A46, take the exit marked "A45", then take the left at the roundabout. Ignore the left turning on the slip and you'll eventually merge onto the A45 west.
Turn left at the roundabout with the fire and police stations on the corners. It should be marked Canley and University.
Go straight over the first roundabout (second exit), and left at the second (first exit). Follow the road down until the left bend and take the second right through the barriered entrance. Follow the road down, bearing right through the barrier. Car Park 4 is on your right down this road, or you can turn right at the end, then second left (not the barriered one) for Car Park 10. Both should be free at weekends.