make a mould for the square pavers out of timber and free form pavers out of sand in the location where you want to use them and pour cement into the mould and hand shape to round them on top, dry and then scrape the sand away and add soil and plants..you could also line the sand or timber mold with plastic and turn the paver over when dry but would be difficult to avoid creases in the finished paver) but to get them as white as the photo they probably need to be painted (also easier to keep clean) ...it would be very heavy job with lots of hard work to manage the amount of concrete needed so the easiest option would be to employ a concretor (with all the necessary tools and experience) but consider white exposed aggregate for a bright non slip surface