A self storage unit can be two different things. If you rent a self storage space in a large storage unit, you will typically find what appears to look like a large garage. This large garage is then sectioned off, usually by concrete walls to the ceiling, and then large hanging garage doors are installed at the front of the unit. This type of storage is usually in a secured and gated area that you can access with a passkey or code. You can usually rent storage units ranging from the size of a closet to the size of a large room to store your items you no longer need or use. This type of self storage may be climate controlled, which usually costs more than a storage unit that isn't climate controlled.
Another type of self storage has been discussed before. It is a portable self storage unit that is brought to your home, you load it and then it is driven to a secure location where it is stored in a climate controlled warehouse until you need it.