Hi, I’m just in the middle of re-doing my back garden, I have had some slabs laid but they are about 3”higher than my lawn in places so want to raise the level of my garden to meet the level of the slabs. I’ve read that laying turf over existing lawn isn’t a great idea so wondering if anyone can point me in the right direction. I was thinking of digging out any big weeds I can, , spraying some weed killer over the lawn, aerating my existing lawn Then putting topsoil over the top. The topsoil will be roughly 25mm-50mm to level the lawn up then New turf over the top! Will doing all of this keep my new turf nice for years or will it just die quickly? Any help would be appreciated.

Many thanks