2 X 4's are layed out 16" O.C.
use a Pressur treated sole plate
and a double top plate.
With the outrageous costs of building material OSB is a very good substitute for CDX Plywood
OSB has proven to be very strong even when exposed to weather and swells up.
When building the gable walls I always frame in the overhang, it is much easier to do it when the wall is on the ground than when it is standing.
Over the 16' garage door opening I always use 2 X 10 Douglas Fir.. When the walls are all framed and braced off for squareness it's time run the ceiling joists and rafters.
Then the rafters are cut and installed 16" O.C. Nailed to the ridge board and toe nailed to the top plate.
So many people use trusses, they are great for the right application, in this case the home owner wanted as much space for storage as possible.
Of course now they make trusses in all different styles so there are many more to choose from.
Once rafters are done it's time for sheeting the roof. With rafters 16" OC you can use the same OSB as you did for the walls. Trusses are run at 24 " on center so either 5/8 with clips, or 3/4 must be used.
After the roof is sheeted and nailed off cover the whole thing with 15 lb black felt paper, drip edge and then shingle using a good quality asphalt shingle.
Once the roof was done, we installed the garage door, removed all the braces and this job was done.
The home owner installed the siding.