The basic rules are that there is a minimum tread width of about 200mm and a maximum rise per step of about the same size. So on a basic single flight of stairs you need the same horizontal distance (if not more) as the vertical distance you want to descend eg. If you are 2m above the ground, your staircase will land on the ground 2m (if not more) away from you.*
I can build open or closed staircases, landings, walkways and ramps, but do not have the facilities to build curved or spiral staircases.
* By using Pythagoras theory you can work out exactly where your staircase will land. The height is y the horizontal is x determined by the width of the treads you want multiplied by the amount of treads required.