Before you do anything else you need to make sure you put the right size cable in. As you have already forgotten to lay a duct under patio, you must consider how much power do you need in the shed, how big is the shed. Is it just a garden shed for a few tools or is it a shed and workshop. Is there any requirement for fixed power tools or heating or is it just plugging in the occasional hand tool. These all have an impact on what size of cable you need. More power needed means bigger cable needed. If it is just occasional use, lower power hand tools it may be easiest to just put an external weather proof socket on the outside wall of the house and plug an extension lead in when needed. If you do need permanent higher power items or heating its probably best to avoid overhead anyway as it will need a heavier gauge cable. Is it possible to bury a longer cable length around the perimeter of the patio.
Doc H.