Basics first

Hi all. Just got a new build house. Nothing in garden apart from a heap of top soil probably covering up a lot of rubble. Wanting to lay a new lawn, would I be best to dig up and level out or can I lay a lawn straight on top of soil.? I reckon I ve got at least 18 inches of top soil in most places. Is this too deep? Thanks Brand new gardener

Topsoil can never be too deep, no. More of an issue is what's underneath it - you could have a pan of compacted rubble which would prevent drainage.