All parts fit together with the main unit no difference between the extension kit and the storage shed kit. Pros: Easy to assembal, perfict match.

[This review was collected as part of a promotion.] I have a 6415 shed which has been expanded 2 times with no problems. I put it together Jan 2017 this 3rd time when adding the expansion kit Jan 2019 the side panels where 1/2 inch longer than the original. I was told by Darwin from customer service that polyethylene plastic the shed is made of your shed may have shrunk to the point where the new parts do not match up with your existing pieces. I was told to lay the new panels on a hard surface for a few days they need to go through what is called thermal cycles to shrink Now why is there any reason this is not told to the customer that the new expansion kit is longer and has to acclimate. If this is so I'll have to pull one of my panels out measure it and wait till the new panel is to size. I'm very dissatisfied of the fit and was not told before I took the shed apart. Other than that I'm very happy with the shed its well built and when it's put together it's very sturdy. Just make sure you buy the size you want and don't add a extension kit it will make your nice shed look like it was built half hearted. Just one note the roof panels where to the exact size of old roof panels.

Extention worked well once I figured to put it in. The rep told me to insert it as the last piece. I found the directions and they told me to insert it prior to the end.