Soil, what to do with it

Evening folks, my first visit to the forum happens to be a question.

I have been working on the garden at my new build property now for a few weeks. Got my ideas for what I want, and busied myself building the hard areas .... a wall and deck area.

Now its come time to decide what to do with the soil to level it out for a split level lawn. Trouble is the soil isnt the greatest and think I would rather ask some opinions on what would be best to do with this. As with most new builds its full of rocks for a start within the top few inches, with a subsoil of clay. The level has been split nicely, and two additional drains were added (perforated pipe with a gravel bed/surround). One drain on top, one drain on lower level. The area around the deck has the drain running right under it and the area there has zero flooding so I am happy with this. The two areas I wish to make into lawns however have this soil that is causing issues. The top layer is rocky and whilst not clay, it does bind together very toight restricting the ability of the water to get through to the drainage pipes. This is causing a small amount of water to stay on surface.

My questions are:

1. The soil itself - is it worth tilling it and adding some organic matter into it, before adding topsoil, sand and turf? If not - then ideas would be helpful

2. Drainage - the tilling would sort the soil and allow the water to drain into it, but should I add a few additional gravel channels to it to help feed the drain?

Pics of the place can be added when I have the permissions :D