cold bridging at flush eaves

Hi all, about to start building and am looking to get my ducks in a row so im just looking for a second opinion on the above..2 storey house, cavity wall construction (100mm block, 150mm cavity incl 125mm pir, 100mm block) with 300mm attic insulation..trying to avoid cold bridging and to have flush eaves so I was wondering what if I was to close the cavity with a slate or similar thereby reducing fire spread but with limited cold bringing and in order to give the wall structural stability and spread the weight of the roof uniformly i put a wall plate inside and outside (outside one might be a 3x3 so as to allow room for a cement board and expanding metal on outside). Could use eaves vents to ventilate the attic. the Attic insulation would only be the thickness of a slate away from the pir board and if the trusses were strapped to both wall plates it should spead the load more universly..

As I am not a civil engineer Id appreciate any opinions anyone could offer on this