Cathedral Ceiling Plaster

Hi Guys

As per the attached drawing I have cathedral ceilings to be plastered. However at the top you can see that due to the size of the ridgebeam required there will actually need to be a flat spot because the beam is deeper than the rafters. I intend to have steel ceiling joists run perpendicular to the rafters to support the plaster. The question is ... should the plasterer have a spiffy method for supporting the plaster along that flat section (maybe using some steel battens with some special fixtures?) or would I be expected to run timber battens across below the ridgebeam (sort of like mini colar ties I guess)?

long furring channells parrelel with ridge at a height to allow short bits across ( make sure all bits are parrelel,straight and level). Narrow top piece of plaster first then ceiling sheets, furring channels can be used on rest of ceiling too with the relevant plates they can be adjusted for unevenness of timber rafters. See Rondo w'site ( google ). You can also probly get an obtuse, internal bead for the joins so they are nice and straight. Dunno if I need to say this but when stopping-up, use a light to look for holidays etc. in topcoat as ceilings seem to show unevenness badly