you could consider actualy having a lot of decking and just go betwween any roots .have you seen those raised walkways on deckin that seams like its floating in a lush garden .i think you got to do what you got to do . get machinery in professionaly if you have to but your going to have to move some of that bricks and rubbish the hard way with spit and polish . the up side is with the machinery while you got it you can easely change levels , dog ponds etc or haveraised beds . check out my garden on my blog but youl have to find it as ive got loads .you can have waterfalls but itys all done at this stage . i think you can realy make a brilliant feacture of your garden i prtefer iit to my house lol. its worth spending money if you have to and elbow grease but you love it .

I think clearing the area first would work much better, dig out the roots or use a stump grinder and clear the bricks etc also you cannot really till until this is done! You may need to import top soil to replace everything you remove. If you are not planting at once you can still add lots of goodness in the form of Humus and leave it to do its work. If you need to cover it perhaps a mulch of compost or bark?