putting in new lawn

[Stephen 47]

I am putting in a new lawn where there is a "lawn" now. do I need to remove the old grass and weeds before rototilling the area or can I just plow it under?

[roddy]

Good question. I just moved into a new house and the lawn is terrible. It is hilly and full of weeds. I'd prefer to seed in the back as it's a big enough lot and sod the front. Can I just burry it with a load of top soil or will the weeds grow through?

[tomf]

Most of the weeds will grow back. I do not love the stuff but Round up would kill the live ones and the old grass also. laying black plastic over it all will also kill of the old lawn.
I just till an area up but I am not after perfect lawn.