Question
i want to remove grass and put rose plants and shrubs and decorative pebbles into a 4 x 4 m area. whats the best way to do it? it has grass and weeds at present

Answer
You can spray a non selective weedkiller (like glyphosate) over the area. You can rent a sod cutter and strip the area of all vegetation. Or you can pull everything by hand.
A good plan would be to mow tbe area as low as the mower can go. Wait for the regrowth (3 to 5 days) and spray the whole area with glyphosate and wait another 7 to 10 days to allow the chemical to translocate to all parts of the vegetation. Clear out the small areas on which you decide to plant the roses and shrubs, plant the desirable plants and leave the rest to die a slow death.
Did you plan to put down a fabric before the pebbles? If so, you can lay down the fabric good and tight; mark the spots where you intend to plant the shrubs; then cut an X at each site big enough to allow you to plant the shrubs. After you are done planting, trim the fabric and put down the pebbles. Sounds like a neat project.