Turfing over stony soil - advice please

Hi,
I am in the middle of levelling my lawn from a slope to two level areas. The top section is being turfed and is very stony, with some stones (boulders!) being as big as 6". I am planning on removing the top layer containing the stones, covering it in topsoil, rolling etc and then turfing. How much soil should I remove/replace with topsoil if I want a level/ lawnmower friendly lawn?
A

 

hard to say without seeing a pic, but i'd be inclined to put 2 inches (50mm) ontop .... here is a calculator to determine how much you need to buy for the area:

http://www.mulch.co.uk/Products/29/68/Lawn Dressing

if the area is small, perhaps you can add an extra inch .... from what I understand, the grass roots needs a minimum of 6 inches of good soil to do ok

 

Thank you. It's a small patch (40 square metres). Yesterday I was told that a lot of soil needed to be removed and then replaced with topsoil before being raked, rolled and turfed etc. I was quoted £1600 for the job. My dad and I were thinking about hiring a rotavator and a skip to clear the top couple of inches and generally level it, replacing it with topsoil and then turfing. Thanks again