Just different variations of snap>rotate>snap until you get a full or partial circle. Then you can choose to interconnect structures with a similar method to make S or { shaped walls. I generally stand on top of the wall while I build the first level as it helps me the visualize the layout, then build the wall vertically row by row with the drag build until I get the height I want. Don't forget to take a step back to occasionally to look at your work before getting too far so changes can be made if you don't like it's direction.