Raising ridge line

Just put in for planning for a dormer on a 1960's semi-detached bungalow with a gable rafter roof (approx 8m wide), it required the ridge to been taken up to give adequate head height. Planning was refused as it would effect the 'street scene' by disrupting the flow of the building (differing ridge lines). I Have talked to the neighbour and he is willing to allow us to alter his roof to match change in pitch and ridge height of our proposed dormer with a flat aspect at the rear. This would then match opposite buildings which both have raised ridge dormers. It has been suggested by planning that this would solve street scene concerns. Would this be expensive to do at the same time as the dormer ?

Thanks for your help