I have a 10 x 12 Tuff shed sitting on the cement and some shims. I think it is a great shed for the money. If I had a flat spot I would put in another. however because California land can be expensive, a large part of mine goes downhill at a 45* angle.
Just remember you will, unless otherwise contracted for, buy a basic shed. There is no skin inside of those studs, there is no insulation, really heavy machines are going to need a little boost in the floor structure; ask the sales person about the floor loading.
With only a vent in each gable I am amazed at how cool it is compared to the outside temp. I did have it painted pale yellow and the shingles are almost white to reflect sunshine. I do not have any windows in the shed and I am very glad I do not. For illumination I have two 8 ft. fluorescent lamps. They light up the shed like high-noon. The roof/ceiling is lower than a in a home so you have to watch what you put up there.
The roof is the ceiling in my shed. The pitch is less than any home around here. I have plenty of head room (unfortunately there seems to be plenty of room IN my head) and even Glenn can wander around in the shed without banging his head. However, you probably will not be able to work with your back next to a wall except at the gables.
Watching the two men build the shed was like watching a choreographed dance routine. One time guy "a" was down on his knees working, almost facing away from buy "b." He didn't even look up, just stuck his hand out and the block that "a" had already thrown went right into his hand. I wonder how many times they had assembled these things.
The shed has had no leaks and no settling. My slab had a definite slope to it. I was working with clay at the time and I wanted to be able to hose it off. They compensated for that quite easily. One corner of the slab was mitered so one corner of the shed was left to hang out in the air. That corner was down 4" to the ground. The men took care of those problems easily.
I am a happy camper with my shed. I use it for storage. If you want pics, let me know.
First of all you have to be smarter than the machine.