The first and most important step to build a shed is the planning part, without a good plan you probably won't be very happy with your shed in the end.
Always Remember, "A Failure to Plan is a Plan to Fail!
Some questions to ask yourself while planning your new shed.
What do you plan on storing in the shed? This will help to determine the next step.
What size should I make it? To store all the stuff you plan on putting in the shed.
Location, is there enough room for the size of building that you want?
Type of shed foundation, 6X6 runners, wooden posts, cement blocks, concrete slab, or concrete pillars?
Shed zoning restrictions, are they allowed, do you need a permit to build a shed, are there size and height restrictions?
I can't help you with the size, style, or shed zoning restrictions in your area but I can help with the type of foundation, framing, siding, or roofing options.
Well maybe I can help with the size, I drug everything out into the driveway. Here I am with a riding mower, log splitter, snow blower, wheel barrow, tow wagon (for mower), push mower, string trimmer, leaf blower, and all the other stuff I plan to put in "my" shed.
This shed could end up being a lot bigger than I first thought. Anyway you get the idea, a little planning can go a long way once you decide to build a shed.
Build a Shed Foundation
The best built shed in town isn't worth a hoot unless it has a sound foundation.
Don't build your shed in a low area where water tends to runoff or collect.
Smaller sheds can be built with an on grade foundation using 6X6 pressure treated lumber or solid concrete blocks.
If using treated lumber make sure to get the type rated for ground contact, the type rated for above ground use will rot faster if placed directly on the ground or buried.
If using cement blocks make sure to use solid ones as the hollow (wall type) crack.
Larger sheds (say 200 square feet or more) require more permanent foundations.
These are usually built with concrete piers or treated wooden posts extending below the frost line.
The frost line where I live is 42 inches, check with your local building and zoning department to find what it is in your area.
Let it Breathe
If you build a shed too close to other structures, fences, shrubs, or trees will not allow it to dry out when the wind blows and the sun shines.
Leave enough room to comfortably walk around it, plus it will make it easier to paint.
The bottom of the shed needs to be at least 4 inches off the ground to allow for air circulation underneath.
Use Treated Lumber on Floor Framing
Only galvanized nails should be used in treated lumber.
If you aren't using a floating concrete slab for a shed foundation then you should use pressure treated lumber for the box sill, floor joists (on 16" centers), and floor sheathing.
Never skimp on the framing lumber for the shed floor 2X6 or even 2X8 lumber should be used if planning on storing heavy items.
This lumber need not be rated for ground contact.
Tongue and groove treated plywood is expensive but should be considered because of its ability to resist rot due to moisture. Lets face it, an outdoor shed floor is going to be wet from time to time.
If you are storing heavy stuff such as a riding mower then 3/4 inch tongue and groove should be used for its strength.
If you're building a shed on a concrete slab then pressure treated lumber should be used on the bottom plate.
If building on treated floor framing regular SPF#2 framing lumber should be used.