For 10 hens and a roo, it's oversized, unless you plan on spending time in there with them. Though you could partition it, using the other side for feed and supply storage. Hmmm, in that light, it's got some good possibilities.
You don't need a foundation. The shed can sit right on the ground. But, a foundation provides a level and stable base, which on a flimsy shed like this is very important. The foundation does not need to be fancy. Nothing more than some boards and four stakes pounded into the ground would be quite sufficient. A dirt floor for the birds is just fine.
With a run to get out into, heat and cold are not a problem with a metal shed. A white metal shed doesn't get impressively hot anyhow. Easily ventilated if you wish it.
Rust and corrosion will be your enemy. Without rigorous cleaning, muck will build up at the base and rot it out in a few years. An application of something like bed liner material around the lower one foot would go a long way towards holding the rust at bay. You can get bed liner material from
Walmart and slather it on with a brush.
If you've no experience with metal sheds, they are very noisy. They boom in the winds quite nicely. They are flimsy, and have a habit of collapsing in heavy snows. The doors forever jam and fight opening. They rust up nicely in a few years. But, with care on installation and some maintenance, they can work well for years.