The first person that comes to mind is Bill @ 5th Gear Motorsports in Richmond (Westminster Hwy.) He has extensive experience in building old bikes into rat rods, bobbers, cafe racers etc. I understand he does all his welding and fabrication in-house but I might be wrong.
My only other suggestion is Cypress Motorbike in Delta. Dave and Darcy went through my SR500 quite thoroughly and they specialize on older bikes (re: anything old and carb'd.) I can't think of any other shops in town who can do such work. Their shop rate is $84/hour which seems to be average. I would think its roughly the same with Bill at 5th Gear. Good luck!
Since the season is pretty much coming to an end, the two aformentioned shops should have time/space to work on your project throughout the fall and winter.
Oh, and no "build" thread is any good without any details!