Well I would certainly set out from the lowest point of the room so that if you have to do raked cuts you will know what your biggest and smallest raked cuts are gonna be at the bottom and you do the same thing above the datum line... ie find the highest point in the ceiling and do the same. You can then play about with it, moving the grout lines up or down until you get the best outcome around your obsticles and good cuts at the top and bottom. So the lowest point in the room is as good a place as any to start tiling as long as the setting out is the best you can get it but I guess you could start anywhere. There are other ways of doing it but if you are new to it and not sure where to start it is a good point of reference. This is just an overview of how to set out using this method. I was taught to the British
Standard of setting out but I realise there are quicker ways once you get used to what you are doing. If you want to know the full method paddyh2 pm me because it is a bit more detailed than I have said in this post.
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Spot on sWe cheers for that