We have just moved into a new build house with grass laid fence to fence. I am planning to put in new flower beds. Would building them in a no dig way (cardboard and then thick compost etc) over the grass work for flowers, as well as it does to create vegetable plots?
I suspect that the soil underneath the grass is a minimal layer of topsoil and that underneath that, who knows what lurks, but the likelihood of it being compacted from building is high. I would rather improve it gradually via no dig than get in there with a rotivator and destroy what little soil structure there is though.
Your preference is good, I would card over then compost and plant, worms etc will gradually colonise the soil again.
I would first remove any rubble on the surface and make it an even surface at least.