I will be constructing a simple 10' x 10' outside storage building in
my backyard this summer. A 4" concrete pad has already been poured,
and as I plan construction, I am considering exterior siding options.

The storage shed will be a pretty simple structure; wood-framed walls
on 16" centers w/ 1/2" plywood sheathing.

I like using "rough sawn plywood". It's like T-111, without the grooves.
Rough sawn plywood is commonly used for the underside of roof soffits, so
it's usually easy to find.

(IMO, Standard grooved T-111 makes a building look like an apartment
complex, and is only as strong as the thickness in the grooves).

One of the advantages is it serves as both sheathing and siding which
makes the walls faster and less expensive to contruct.

It comes in various thicknesses from 1/4" up to at least 5/8", depending
on the strength and span rating you need.

It's a standard wood product, so it's easy to cut, nail, etc. It takes
paint well, but I prefer to use an opaque stain. I spray on the stain for
ease of application, since the rough texture is hard to roll or brush.

I used the rough plywood for our shed (now over 16 years old), our
garage, our pumphouse (18 years old), and our house. Here's a few example
pictures:

www.mountain-software.com/siding1.jpg
www.mountain-software.com/siding2.jpg
www.mountain-software.com/siding3.jpg

I use metal "Z-flashing" at all horizontal joints, and caulk all vertical
joints using polyurethane caulk (PL Series available at home centers).

I try to keep all wood AT LEAST six inches from the ground, though my
shed and pumphouse are on 4" slabs and haven't shown any rot problems in
18 years.

Try to control water/mud splashing up on the walls by installing gutters,
or putting gravel or barkdust around the building.

Of course, annual maintenance (washing the walls, repainting when
necessary) helps a lot too.

Hope this helps,

Anthony