your local home center will have a nice assortment of pull down stairing that works great. you can then mitre some molding around the stairs to finish it off and custome cut the angle on the bottom rung and have a good dependable set of stairs.
First you need to measure the opening or the distance between your ceiling rafters. This would not be the OC measurement but the actual space between each rafter. Then purchase accordingly.
Also, your stairing must fit PARRALLEL NOT PERPENDICULAR TO THE ROOF RAFTERS.
You do not want to cut any rafters for this to fit.