I have dug out the top 2 or 3 inches of soil, grass and weeds, i've tried to remove a huge ivy type bush/tree but some roots still remain they span the entire garden space. My plan was to put 2 or 3 inches of top soil and then turf over it. Will the roots that i'm unable to remove affect the turf through the top soil? Should i use a "weed barrier" beneath the top soil? Would spraying the soil/weeds with "Roundup" before putting top soil down be a good idea? Thanks in advance.