If you're going to go through the trouble of placing a metal box that weighs several thousand pounds in your yard, you should start by making sure your local code enforcers aren't going to promptly make you move it.
As of this writing, I live in Austin, Texas. Codes vary substantially from place to place, so you'll have to verify for your own locale what the deal is.
Here's how I found out I'd (probably) be enforcer-free:
google: Austin city building code
click on first result, go to some Austin city webpage
click on 'frequently asked questions' then 'inspections and permits' then 'permits' then 'do i need a permit?'
sweet! under 'work exempt from permits':
"Building One-story detached accessory structures, provided the floor area does not exceed 200 square feet (18.58 m2). Please keep in mind that although you do not need a permit to build or install the structure you must still abide by any zoning rules and regulations in regards to height, setbacks and trade permits. If you decide to install electricity or plumbing systems into the structure you will be required to obtain those trade permits. Please visit the ‘Zoning’ page to find out what which regulations apply to your home in regards to structure height and/or yard setback areas."
I want to make sure I'm ok on my planned rooftop deck, so on to the zoning page. Yikes: forget it. I'll just do it and take my chances. I think I'm supposed to be at least 5 feet from my neighbor's fences or something.
If you can't avoid zoning issues through an exemption, you're in for a process. Check out what others have done for inspiration/examples. The good folks of The Shipyard, a collection of workspaces consisting largely of shipping containers in Berkeley, California, have been so kind as to publish their use permit details. You can check it out here.