I would like to add a suspended ceiling that will go in my office - probably something like 20cm over my existing ceiling. However, it will stop around 20cm from the edge all the way around (not sure what this is called). I was planning on using plasterboard for this - but how would I finish the edging? I would also like to put lights "inside" the lip of the ceiling to give a warm glow to the edges of the room. Any ideas on which to use (the ceiling will be quite big - around 2 by 3 metres). Thanks.