How much topsoil

Hello. Gardening virgin here. I'm sure there is a general rule of thumb for how much topsoil to use, but I don't know where to start.

I am replanting my back garden after it got destroyed building an extension. After raking the bejaysus out of it, it is still a little uneven and the garden slopes slightly, so I'll be using more topsoil on one side than the other to level it out. I'm not worried about rotavating it, as I don't need it to be absolutely perfect.

The area I am replanting for lawn is about 6 metres wide by about 10 metres long. I have raked out the stones and put Round-up rootkiller on it a few weeks ago. Everything is dead, so I reckon I better get planting again.

How much topsoil should I order (by the tonne?) and how much depth should I lay down?

Any advice appreciated, thanks

Hi,

I was in pretty much same position after extension 2 months ago.
Garden area left was 5m x 10m
I bought 3 tonne of topsoil, levelled it, de-stoned,lightly raked it and just 'walked' the topsoil in.
Instead of replanting, I bought some sod (55sqm) and rolled it out.
2 weeks later I had a perfect lawn so perhaps an option for yourself?

Hope it helps,

Brendan.