Hmmmmm, are you thinking of using the raised beds around the periphery, to deal with the poor soil? The trouble you have is that you'll need to make 'em really quite deep for things like shrubs to raise the whole root ball above the rubble, and then you face a lot of expense in terms of both materials to build them and soil to fill them. You'll have to think about how they are 'backed' and how they work with existing fences, hedges etc. Wood, even pressure-treated wood, will rot eventually when in contact with soil, so the only durable way to do it is to use brick or stone. And don't underestimate how much topsoil you need to fill even a 30cm deep bed - it can be £££ across a whole garden!
Another thing - unless you're going for a very formal, symmetrical look in your garden (which is actually one of the hardest things to achieve - the quality of landscaping tends to be very 'exposed'), putting even-width rectangular raised beds all around the edges can look just a bit 1970s! (Think: carpet bedding planted in neat lines). They do work brilliantly if they are evenly spaced across a larger area and used for veg gardening, but this is often a more functional and less ornamental way of growing than some people might want in a back garden. If you pinterest something like 'shade garden', you'll probably get loads of images of curvy paths for this reason.
I know it sounds like a lot of work, but in the long run it might be easier to work in sections and dig the rubble out to a depth of two spade heads. You can then improve the soil you already have by adding grit, manure, and compost. It will be considerably cheaper this way, and you can choose whatever shape you want for your beds, including curves which can be really useful as a way of breaking up a standard rectangular back garden! You'd be surprised how much you can get done if you go at it together as a family and tackle a bit each day.