Any shed or garden building will require a foundation. This is essentially a durable base that will support the weight of the shed to enhance its longevity. It is important to make sure that the foundations are robust, otherwise, your shed will suffer as a result and you will likely find that it does not last for as long as anticipated.
If you have a patio and you intend on getting a small shed, a base will not be required as the surface already available will be sufficient. However, sheds 8’ x 6’ and bigger will need to be installed onto a foundation. Those on the smaller side can be placed onto timber, patio slabs, crushed stone, etc. Those on the larger side will require something more substantial. For example, you will likely need to create a base that is made up of concrete slabs.
Before deciding on the correct foundation, you will need to evaluate the current state of the surface that the shed is going to be placed on. Sloping ground makes things slightly more challenging but creating a base is still doable, it will simply require more thought.