Hi,
Are you re-seeding the grass or laying turf? You will need to give the earth a few weeks to recover from any pesticides before laying a new lawn.
Round up will kill off the grass & anything else that it is sprayed on .. will take around 2 weeks to die off... assuming that it's dry, you can then "set it alight" to burn it off.
Once you rotovate it, you should roll the earth to level it. (you can add some manure to give the earth some nutrients at rotovating time), make sure you have enough top soil & rake till you have a fine tilt & no stones or pebbles... Apply grass seed as recommended... don't let the earth dry out, so check it every few days & water as needed... let the grass develop well before cutting & when you do cut, never take more than the top third off... even less if possible... Don't apply any fertiliser till after a winter season has passed...