I agree with Mark, don't resize or change the size dimensions of anything, just shorten them to the lengths needed for your size building.
A pure traditional timber framer would be upset to hear that you've gone to all the work to cut the joinery on a frame and then side it with plywood.
Have you looked at the price of plywood lately? Boards (1") are now cheaper than plywood! And it will give the building a more traditional look, even if only from the inside.
Just my 2 cents worth.
Jim Rogers