make steps leave from an ellipse

hi, everyone! i'm having a problem with this definition. some friend here have helped me, but it contains some errors and i don't know how to correct them.
i have these surfaces and they must turn to a huge bleacher and the steps of the bottom must have the confortable height to sit on and as it goes to the top it should softly decrease. Well, the definition here is good, but have some problems, i hope someone help me.