Used shipping containers make for great onsite or offsite storage facilities, as they're very strong and durable and meant to protect the items inside. They're also usually very affordable and can easily be transported to a jobsite, warehouse and the like; they are ready for use once they arrive so you don't need to worry about any fabrication or finishing work for your unit. When you are ready to buy a used shipping container for storage, note a few features to look for so you know you get the right one for your needs.
The floor of a shipping container is typically made of thick plywood that is glued into place; while you may not think much of the condition of the floor, you want to note if it seems soft and spongy at all or if there are chips and cracks in the plywood. A soft floor usually means water damage that can cause the floor to become crumbly over time, and chips and cracks can also become larger and eventually need repair. You may want to put down a steel or aluminum sheet on the plywood to give it added protection, but if the plywood is severely damaged, the connectors you use may not hold firm.
Hinges and locking
Check the hinges of the door to any shipping container and note if they're in good condition; if the hinges are rusted or damaged, you may struggle to get the doors open or they may not close entirely, which means not being able to actually lock and secure the doors. These hinges can be expensive to replace since they're heavy-duty and need to support the weight of the metal door, so it's good to ensure you choose a container with hinges in good condition rather than assuming you can easily have new ones installed.
While shipping containers are meant to be very durable, this doesn't mean they won't suffer rust and other corrosion over time. Step inside a container and note if you can see daylight coming in through any parts of the walls and especially around the connectors. If so, this means holes that may allow in rain, snow and other moisture, possibly putting your stored materials at risk. If you will be storing items in plastic bins or barrels or another waterproof material, you may not be concerned about this risk, but for most buyers, you want to ensure your used container is waterproof with no damage or obvious holes.