Planting/ Topsoiling over turf

My front garden is on quite a slope which follows a shared driveway. What I am hoping to do is to build up a wooden bank and put topsoil down to level the slope off. My neighbour has said that I don't need to remove the existing turf (it will become a flowerbed in this area). Can I just cover the turf in 6 inches of soil and plant away, or do I need to weedkill it / cover it in a fibre mesh to kill the grass. It's quite a large area and would be a complete pain in the bum to dig up the existing grass, so covering/killing would be a better option.

We hope to mesh it and then lay slate chips ontop.

Any ideas?

Grass will come up through a couple of inches of soil but not a spade's depth or so, so you just need to make sure you have it all covered to an adequate depth - 6 inches should be OK if there are no thin spots. Give it a hard cut first so that there's less chance of voids in the covering.

I've always dumped any redundant turves in the bottom of a trench when digging and they don't come up ;o)