The easiest way to do this is to make a sketch and take it to your local truss company,
they would supply the gable 2 trusses and the valley set that goes on the roof. If your old roof is built with trusses, you will need their engineer to tell you what needs to be done before you cut them off unless they are just long tales sticking out. 2 2x10would be pleny for each beam. Usually the beams are cut into the wall or hung off the wall top level with the top plate, finding bearing can be tricky, setting them on top would be easier but generaly you want to keep the gutter level but a raised deck cover looks good too.
6x6s will do the job just fine.