Hi John and welcome to GoY. You are going to have to remove the grass roots or they will simply keep growing... As for breaking the soil up, once you've removed the grass roots and any other perennial weed roots (eg dandelion) you can dig in compost or soil improver. Alternatively just spread a good thick layer of compost or soil improver on the surface and let the worms take it down into the ground. Just make sure you've got all the perennial weed roots out first or they will have a field day. You need to keep hoeing the annual weeds off, weed seed can sit dormant in the ground for years and then suddenly start to grow. Good luck and post up a blog or two as your garden starts to grow.

thanks you I was hoping they would rot down as I can leave it for a year as i have plenty to do outside and in. thanks again.Never mind i'll have to work faster or get the wife to do some weeding i'm sure she wont mind.

kind regards john

Unfortunately grass roots don't rot down they simply grow...

I don't think you can achieve what you want without too much labour. Gardening isn't like that - you will have to get all the roots out and make a start on breaking up the ground. If you leave it rough over the winter the frost will do some of the breaking up for you.
However,if you could get hold of some of the black plastic farmers use for wrapping haylege (or even some old carpets), you could lay it down over the soil for at least six months, preferably longer, and then the weeds underneath will try to grow and they will die through lack of light. I have used this method very successfully on an allotment but it doesn't look very pretty in a garden and you would still have to break up the soil afterwards.