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