Locate and purchase a new or used shipping container. Coordinate the delivery and equipment needed for setup as needed. Most sellers offer these services.
Build a foundation to keep the container approximately 6-inches above the ground to avoid moisture corrosion. You can do this by digging with posthole diggers, inserting forms and pouring concrete to create 12-inch diameter by 18-inch deep concrete piers with 1/2-inch embedded bolts extruding approximately two inches above the top. The piers must be installed at a uniform height and should be approximately 12 inches below the ground surface. Backfill dirt as needed when the concrete dries.
Use heavy machinery to move the container into location on top of the concrete piers, and secure nuts to the embedded bolts with wrenches.
Remove all existing paneling or flooring, then repair and clean the interior of the container as needed.
Use a table saw to cut one-inch plywood sheets as needed to create a new sub-floor on top of the existing metal floor frame.
Snap chalk lines on the wall panels at all new door and window locations.
Cut through the panels on these lines with the angle grinder. Smooth all edges as needed.
Cut steel angles to the desired length with miter saw and insert them into openings from the exterior side to create trim for the doors and windows.
Weld the steel angles into place to form a metal trim lip and frame around each rough opening.
Build walls inside of the container with studs. Cut the studs to desired length using a miter saw. Attach one stud to the floor and ceiling of each wall to create the top and bottom plates. Then, start in the corner and attach studs onto these plates and the wall panels with screws at 24-inch intervals. Frame jambs and headers around the wall openings as needed.
Install the pre-hung doors and windows into the framed wall openings.
Install all of the electrical receptacles, switches and wiring. Coordinate with an electrician if necessary.
Insulate all of the walls with fiberglass, rigid foam or spray-on expanding foam insulation.
Attach the dry wall, or other wall covering material, to the studs with screws. Install interior wall, ceiling and floor finishes as desired.