The point I mentioned earlier is the colour. The last car in that colour was 2005, and would be worth about £5k so probably not that many takers to buy a roof at 20% value of the car.
All newer cars need to include the respray costs, aprox £150 - £200.
So for most people the top would be £1200 once received. This is assuming a 100% in new state unit, compared to the new units available in Germany for less than half the price.
If it was a newer colour / or more common one, you can obtain a higher price, otherwise I would be thinking more about the £650 - £700 range which opens the door to other colour users as well.