Raising the level of a lawn

I have an existing lawn adjacent to a raised patio area. The lawn has been in a poor condition, patchy, balding and weed ridden. I would like to raise the level of the lawn to run flush with the patio, +3" to 9" varing over the area.
I have completely stripped the top layer of grass and just started to turn over the soil bed. Once I had finished turning over, I had planned to roller the soil? wait 2-3 weeks to check for weed growth, spot weed with an instant biodegradable weed killer then add topsoil and finally turf.
I'm happy with adding top soil and turfing but concerned about turning the existing soil.
Is this necessary when adding 3 to 9 inches of soil and turfing, will the weeds work through?
Could tuning over the existing soil (down about 6" deep) and adding top soil hinder the turf from 'taking'?
I will be looking to lay the best quality turf and want to achieve the best possible results. Im not too concerned about time and would appreciate any advice before continuing.
Thanks in advance, Mark
B.T.W The old lawn drained well and the area is 35m2.
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Marko


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