I'm getting ready to replace my existing weed infested mess with tif 419.

My plan is to remove the existing mess and lay in 2 to 4 inches of high
quality topsoil.

Most folks have suggested I hit it with round up that assault with a
rototiller and rake it out. I really want to get a fresh start with this
lawn and get rid of everything (most seems to be weeds). Will there be any
residual effects from the roundup on the new sod?