Hope I might be able to get some ideas or recommendations...

I have patch of land around .5 acres, south facing and sloping at
around 35 degrees (going up from my property) to a height of around 30
feet to a hedge and substation the other side.

The land is composed of a rough soil mixed with bricks, coal ash /
clinker and stone. The only things growing are dandelions etc. The
depth of the waste appears to be at least 6 feet (I believe its from
an old mill clearance, bulldozed out of the way in the 80's to build
the houses), so clearance to 'real earth' is out of the question.

The land has had Japanese knotweed on it which has (after 4 years of
work, lots of weed killer and a large garden incinerator) been brought
under control, so clearance off site would not be practical given the
costs likely for disposal

So - my problem is how to develop the land to garden. At the moment my
thought is to terrace into levels and put a layer (12 inches ? 18
inches ???) of compost / soil and grow in that. I am really not sure
how to go about this - can anyone advise on the correct levels of
compost / soil I would need, depths to work to, or recommend any books
for developing a garden on what I suppose is a 'brown field site'.

Or for that matter, any other thoughts / ideas from the gardening
community on getting this land workable ?

Thanks in advance

Steve