How much should a contractor charge me for a 32' x 32' second floor on my garage with8' walls 2x6? Roof 6/12 scissor trusses 1/2 plywood? 17 trusses 2' centers?

and 7/16 osb for the 8x32' walls and titanium roofing instead of felt paper.

There is no way to tell since we don't know if you are on an island in the Pacific or in South Mississippi. Simplest thing is to get 3 bids from contractors. As an alternative, you can price individually and then get labor only bids. You can also Google "approximate building costs" and find a lot of info. With a 32 X 32 above loaded, you will also have to consider additional support below. Average building costs as a guess $85-100 per sg.ft. bare walls. With a 34 ft. truss you will most likely need some crane rental time.