Lots of variables here....I have never had one prebuilt and delivered nor purchased a kit, I have always bought materials and built my own design. My neighbor recently had a prebuilt one delivered and set in place, he was able to order it with siding and roofing that matched his house. But you pay dearly for the convenience of having one built and delivered or one constructed on your property.
Not to knock the big box home stores, but I think their kits skimp on materials and only meet minimum standards. The ones that use 2x2 framing and 3/8 OSB sheathing are a joke. When I built mine it used 2X4 framing and 1/2 plywood sheathing and was strong enough to have an upper storage floor above the ceiling height. Just my nickle's worth.
If you have little carpentry skill and have to have one built or delivered I'd choose the prebuilt type, because you don't have the materials exposed to weather and you will know everything is already there...hope this helps.