I always thought these markings were made by machines, until I saw some people draw them by hand. Turns out, you can make near perfect road markings with a movable can of paint. If you use GPS to trace out your track, you can just fill them by hand.

As for construction, here’s a timelapse of making one using stone tiles: youtu.be/gXiOt-9WCag

Here’s one made of asphalt: youtu.be/DORBEGYVgYE Note the pre-poured blocks of concrete in the center, which likely help the round shape.

In this video you can see the imperfect temporary road markings for a short moment: youtu.be/SV2vSL_hiA0

This video showcases a different style of roundabout that makes two-lane roundabouts a bit easier. Note the two round, concentric lanes separated by concrete barriers: youtu.be/iRclLOgN-xw

This video showcases the manual driving work done to make the round roads: youtu.be/KCQv24BkI6Y This is a four lane roundabout. The video also shows how the line markings are applied (by a spout, in a car).

This video shows a prefab concrete roundabout installed over a weekend. All they needed to do was prepare the soil, lay down the blocks and paint the lines: youtu.be/J-BZWfbygkc

This video shows how the center concrete slabs can be laid on location using a specialised machine: youtu.be/J2g0JZzqbAs

I’m not sure if this tech is applied, but farmers use millimeter precision GPS to efficiently farm their soil. The GPS receiver itself costs a couple of grand, but making a car in a closed-off road drive in a perfect circle is hardly a technical challenge these days. That said, these people can probably do it by hand and you wouldn’t notice the difference.