Repeating transformations (move+mirror+rotate3d) automatically

Hi guys,

 im developing a stair based on the relative angle of a step with the previous and that they align on the outer limit. the thing is im not seeing a way of repeating the process an x number of times automatically, without having to add a new step by individually relating it to the previous. I think i need to use the transform component to solve this but the changing index of the vertice i need to use keeps me having to find it by hand at each step.. why does the index order keep changing? If anyone has a suggestion it would be very welcome

Thanks in advance ; )