I have a small chimney breast in my new house - more a flue than chimney. It
is only 1 brick deep from the back wall, but unfortunatly its not in the
middle. As i am putting an LCD on it i want to make it look central to the
room. I am planning to extend it to one side by around 250mm using stud
work/plasterboards/plaster.
The question is do you build it such that on the outfacing wall the stud
work is flush with the current plaster or (as i think you would) do you
build it such that its ~3mm back from the current plaster line such that
when its plastered its much easer to jet a seamless join?

A pic of what I am looking to do is at
http://www.convery.me.uk/temp/ChimneyBreast.jpg (Red = addition)