Just created a cathedral ceiling in a full house renovation project. Not easy, ceiling ties and rafters meet outside the walls of the house. Got around this by adding 4x2 glued and screwed to the original 5x2's, resting on a glulam beam. I have to double up some rafters with 9x2's, but even these don't meet the top of the walls. Thinking of either adding timber triangles at the bottom of the rafters as 'fig 1' or preferably add legs as per 'fig 2' on sketch. During the construction of the cathedral ceiling, timber triangles were glued/nailed between what remains of the ceiling ties and the rafters, before both sides were strengthened with ply gussets. Does anyone know if adding legs to the bottom of the new rafters (for velux) would be acceptable (to allow a connection from the wall head to the rafter)? Been looking for similar scenarios online but can't find any. 

One for your SE I think.