You will have to tear down the deck and start over, so free that constraint from your design thoughts. You need an architect brain to plan the whole, not consumer software.

Yes, that will all need to be demolished, start with a new foundation for the little area to be added. Just looking for ideas to see what I like so that I have a better idea before going to a draftsman/architect.

STOP NOW what you are planning needs an architect and they design the roof that works IMO vaulted ceilings are a waste of enegy consumption and often look goofy when the rest of the home is aregular height ceiling . The vaults also play havoc with sound and even lighting . This requires a lot of help from a good architect and unless you are one get one.

Start with what your builder proposes. We certainly can't provide any input on your vaulted ceilings.

Consider the vault going the other direction. The trusses may be able to be altered with direction from a structural engineer, or the entire roof structure may be replaced and be easier.

Get cost estimates at several points during the design process from the buider that will be performing the work.