Rebuilding lawn/soil after house renovations

Hello everyone,
Anyone has some advice for me please.
I have a small garden about 25m2. We recently had house renovations and the garden was basically a building site.
Half of the garden has sand, bits of concrete etc. on top of it. How can I prepare it for a lawn? I was thinking of just digging up the top couple of inches but what would I put on it then?
The other half used to have concrete which I got rid of, now I have a 10 m2 square hole with a depth of 20 cm. What do I do with that? Dig it up, turn it over and then order some more earth?
Thanks for any advice.