A small, flat, circular structure f...

A small, flat, circular structure for a Minecraft hub, built entirely in a single block type of your choice (full creative freedom on the material). No tower, no roof, no upper floors, no interior structure of any kind — completely open to the sky, flat ground level only. The circle should be small and compact, not large or sprawling. Around the outer edge of the circle, a low perimeter wall (rampart) 5 block