Don't forget local zoning laws, especially set backs from adjacent property lines.

Depending on where you live, the size may affect your property taxes.

If you just need electric for lights, a solar/battery setup may be easier than running a line. If you run a line and conduit, consider running a low voltage conduit as well, for alarm/phone/internet/cc tv/whatever.

If you might store a riding mower or other large device in it, make sure to make the door big enough.

Consider building it far enough away from the house so that if the shed goes up it won't take the house with it, and vice versa.

Chat with your zoning people. Where I live, we don't need a permit for anything under 200 sqft (12x16 = 192 sqft). You'll fill up a 10x12' shed in no time. If you have a 200sqft max, you might go for the 12x16'.

Check locally for a company who provides formed powder-coated steel roofing to roofing contractors. There's one here that will take your dimensions and provide materials (steel sheets, ridgecap, edging, screws, etc) and instructions for doing it yourself. If two women can put one of their roofs on, you can. Again, talk to a ROOFING MATERIALS company, NOT a roofing company. IOW, shop where the roofing companies shop for materials.

When you add gutters, make sure they tip in the right direction. Allow for spillover with your rain barrels.

Most thieves go through the window or door. If you don't want to invest in a strong metal door, get a cheap one and then ask your roofing materials company (where you got the roof stuff) for a sheet of unformed (flat) metal in the same color as your shed roof, and face the outside of your cheap door with it.

If you aren't putting in windows for light, you'll need power run to it. No light at all will get old really fast.

Plumb, level, square.

Sue

Sue you summed it up very well with those 3 words. I'd simply add "Nahm's" from This Old House advice, "measure twice, cut once". Such a simple thing and so easy to forget when you get caught up in trying to finish a project.

Had a 10'x20' wooden shed built on galvanized metal skids so I can relocate it as I clear my back lot. Installed translucent roof vents that allow light and air in, enough light to easily move around in the shed during the day, also opted for the traditional barn type roof (gambrel?) so I would get more usable cube inside.

I installed double doors to facilitate loading/unloading and it allows a lot more air and light during good weather, also ran metal channel across the headers with a 1/2" plywood floor to give me a loft that I could use as a nice living area should the house be compromised.


Kona1

For security against both fire and thieves I would recomend brick or concrete block construction, not timber.
I would certainly avoid windows.

I would install both grid and solar powered lighting.

Consider storing your supplies in crates topped with a large piece of plywood, this may be utilised as a workbench or table, and in emergency as a bed.

In case you need to hide/shelter/live in the shed, ensure that the door can be locked or bolted from the inside, some types use only a padlock on the outside.

If casting a concrete base for the shed, consider making this bigger than required so as to provide a water/mud/dust free hardstanding.
Consider casting into the concrete a couple of steel hoops or very large eye bolts.
Valuable but portable property such as generators, motorcycles, lawnmowers and the like can then be secured with a padlock and chain.
If under normal circumstances you store such articles in the shed, you may need to secure them outside in an emergency if the space inside is needed otherwise.

Consider a lockable cage of steel mesh against one outside wall of the structure.
A generator could be run thus and provided with ample ventilation, but secure against theft or tampering.

Consider building a bench seat against one outer wall, made of concrete blocks and topped with paving slabs or similar.
This could make an attractive feature whilst providing safe storage for gasoline or propane.

Nothing a couple of LED lights won't fix...

Consider a couple of very small, high "windows" on the walls with best light exposure. Typically this type of celestory [upper] window just under the roof eaves is too small to be an entry point, too high to allow passersby to look in, easier to install without creating leak potential than skylights, and do not interfere with other uses of roof real estate - like solar or water collection. Even putting in a couple small rows of glass blocks will do the trick.

http://www.ag.ndsu.nodak.edu/abeng/miscplans.htm

Lots of plans there for just about anything you might need, courtesy of the North Dakota University Extension Office.