I'm going to be building a 12x16 shed in my backyard which will be a non-permanent structure. I am simply going to frame out a platform which will be supported by pressure treated 6x6x8 timbers resting on gravel. This will be a "garden shed" which will house two garden tractors, a push mower, yard tools, and seasonal decorations. Of course I want it to be built well, but do I need to go 16" on center for the structural members? Would 18" or 20" on center be acceptable for the floor joists, wall studs, and roof rafters? I should add that this is New Jersey so the roof will see some snow loading in the winter.
I don't know about the others, but in 2002, I built a 10x12 shed similar to yours. I used three 4x4x12 and spaced the floor joists on 16" centers so the plywood decking would fit properly. I just measured the studs and they are also on 16" centers so the T-111 siding would fit properly too.
If I recall, I used the hurricane ties to nail the walls to the floor. I made homemade trusses for the rafters (no ceiling joists). My shed is the only thing on my property that didn't suffer any damage after Hurricane Ike paid a visit recently. The eye wall passed directly over our house.