These are the tools you'll need for concrete. Some, like a mixer, are not necessary, but will make a big job easier.
Stairs can be made out of metal, wood, concrete, bricks, dirt. Depends on what you want and where you want it.
Latex concrete lends itself to unique and sweeping shapes that you couldn't achieve with many materials. It is cheaper, but slower than metal, and quicker, but more expensive than poured concrete.
A poured concrete roof is about as strong as you can get. You will be able to walk on it without ever thinking twice about falling through.