Thanks for that. Not that it means much to me at this stage. I was thinking of something like 100 mm display so that it can be seen as people drive into the car park. Power supply - battery is easier as no mains power on this display board, but mains power could be doable but it will obviously cost.
Well any LED display that is even remotely large will draw a decent amount of power so batteries are more then likely out. While LEDs draw litttle power on their own it adds up to quite a bit when there are a thousand of them.
As for the LED displays I spoke of earlier, I believe they are around 70x120mm and they can be chained so they may fit your criteria.