When we bought our house it came with a great shed. Love my shed. It's 12x20 feet and has a lot of storage and a great work bench. It also had a covered lean too next to it. I'm not sure what the previous owners used it for, maybe to park a boat or 4 wheels. We decided to make it a green house. The only draw back was it was facing the wrong direction and was on the wrong side of the shed to take full advantage of the sun, but it still gets plenty hot and has plenty of light.
I wish I had taken more photos of the building of the green house to show the progression, but I didn't.
I had made the tables in the greenhouse a few years ago for various purposes and they worked great for the green house
The only draw back to the tables was that they were too tall. So for our second year of growing I cut them all in half.