I don't have any timber framing experience. I've read all the books I can find, but can't find reference to the "odd" type of design I'm contemplating.

I wish to build a timber frame addition onto my conventional-framed one-story garage. The existing garage is 16x20'. The addition will be a four bent frame, 1 1/2 story, 25x30'. I plan to take off the old garage roof and build on top of the existing structure. One side wall will be built over an existing (strengthened) garage wall. From the old garage, the new structure will extend 6' in front, 4' to the rear, and 9' to one side. Here's the odd part: I don't plan to enlarge the enclosed space footprint, just raise the walls to meet the higher roof, and put a plywood deck on the existing ceiling beams. The extended area will be overhanging roof only.

Obviously, the structure won't be as rigid as one with sheathing on the 3 outside walls. My question is, will it be strong enough?

My big concern is uplift from strong winds under the large overhangs. I live near the coast, so hurricanes are a possibility!

I want a clear span for the front overhang, so I'm thinking of building a scissor truss on top of the posts for the front bent- no tie beam.

I plan to mill the beams with a chainsaw mill from white pine logs, and use 10x10 pressure treated posts set 4' deep in concrete. I'm not sure if that's the best way, or if I should set the posts above ground on piers.

Does this sound feasable?
Any thoughts of advice would be appreciated.