Builders rubble buried in garden

[mkb.]

So I think we’ve made a silly mistake and need some advice on the best way forward. We’ve recently had some renovation work done and to level the garden we had a retaining wall built and the builders rubble back filled the area. There’s enough room for approximately 10cm of topsoil which the builder thought would be ok for grass however we want to plant more than grass and also after researching I’m realising 10cm is not enough for grass anyway.
How should we proceed?
Is there a depth we should dig down and remove rubble to? I’ve seen some posts saying approximately 90cm of topsoil should be fine, not sure whether to remove 90cm of rubble from the full lawn area or just the borders for planting?
Also thinking hiring a digger is going to be the best way to remove such a big amount?
Any advice would be much appreciated
Thank you

 

[blup]

About 4-6 inches for grass or turf. Should be OK for smaller plants and shrubs. Consider pots. Otherwise dig it all out as suggested.

 

[cdbe]

Raised beds.

 

[Odds]

A Zen garden.

 

[morqthana]

Rockery.

 

[Odds]

It all depends on what is meant by 'builders rubble'.
If it consists of bricks and mortar then you could use them to fill in a gap or construct a support wall, depending on the condition and quality of the brick.
I took out a lot of hardcore used to fill in post holes and used them for a moss garden, 'painting' them first with a buttermilk solution to encourage growth - use moss that's attuned to stone rather than wood for best results. I still have three large blocks of uneven shape and size which can go into a shaded corner where little direct sunlight shines and plant things like haircap or glittering wood, then mix in flowering plants for colour.