Ultimately, it depends on how large the area is. In our case, the starting situation was as follows:
The soil consisted of clay and stones and was also compacted due to the construction work. The lawn area is 400 sqm.
I had 15 cm of new topsoil added in total. Check if the soil is good at your place by simply digging a little with a spade. As a result, I think the soil should be okay and can still be used.
My tip: Make it fertile. I was lucky because a nearby compost facility didn’t know what to do with the stuff. I got 10 cubic meters of compost for a flat delivery fee of 40 € and spread it evenly (with a wheelbarrow).
Rent a motor tiller with a gasoline engine and till the entire area. You also work the compost in with this step. If the soil is clayey or the location is shady, work in some screed sand (coarse sand). This prevents waterlogging.
Buy a large rake and smooth and crumble the soil nicely. If that’s too difficult, this works better with a gasoline-powered scarifier.
Turf is not necessary if you do the following: Spread lawn seed evenly, then cover with a very thin layer of lawn soil. Just enough to barely cover the seed. Then press everything firmly with a lawn roller and NEVER let the area dry out.
I did everything as described above in May 2019 and had a wonderfully beautiful lawn by mid-June. Ok, when standing directly on it, it was still a bit thin, but that soon changed.
Since the lawn was being redone anyway, I buried a pop-up sprinkler in each corner of the lawn area and ran the pipes under the lawn. Also think about how the lawn will be used. There is so-called wear-resistant lawn or play and sports lawn. It also tolerates playing children, romping dogs, and the occasional garden party and still looks very good if mowed often enough.