Oil Consumption is a small issue. It's fairly common, but if you do regular oil changes, you might not see much consumption. We have customers who do their servicing every 8000km/6 months, and they are usually just at the min line (1 litre low) by the time they come in for the next service.
What you should look out for is Fault codes for Boost Pressure Regulation. We've seen several B8 A4 2.0T have wastegate issues and end up replacing the turbos. The wastegate ends up wearing out and it will sometimes not stay closed, which won't allow the car to hold boost pressure properly. This would end up giving you random spikes in boost, sometimes overboost and sometimes no boost at all if the wastegate gets stuck open.
If a B8 A4 is what you really want, and you see yourself keeping it for a while, I would buy one that has had the turbo replaced, or budget for the ~$2k that it will cost to replace it and be ready when that day comes. If you're worried about oil consumption, see if you can find a car with service records and see if you are able to figure out by the service intervals if it is going through oil more than usual. If the car is getting serviced every 15,000km and it's a little low on oil each time, then you would have no worries ramping up the intervals to 8000km and probably won't see any consumption.
Source: Work at RPI.