Subscribe to download
Mega Ring Habitat (3.5km diameter)

Warning: This structure requires a lot of ram. If your game stutter and freeze, try closing a few running programs to free up some ram.
If you have at least 12GB of ram and no other programs open, it will run just fine. You may be able to run it on less, but I havent tested it yet.
It may take several minutes to spawn.
Surprisongly enough, it does not have a large impact on sim speed. At least not on my computer, which is 4.5 years old.

This is a ring-shaped habitat station.
I originally wanted to make a ringworld, but of course neither the game nor my computer will ever be able to handle a structure of that size. Instead I decided to make something similar, but a lot smaller. This however does not mean it is small. In fact, being 3.5km in diameter makes this one of the largest things on the steam workshop. Even the 1.25 km long capital ship I've been working on looks small in comparison.
The ring would generate gravity by spinning, but because of the way space engineers works you can't generate gravity this way. Therefore I had to use gravity generators (with minimal overlap thanks to math) in stead. Also, trying to spin it up is not only ridiculously hard, but will destroy the ring. I tried.

Kinda reminds me about the ring thing from Halo.

Some statistics:
Diameter: roughly 3500m
Circumference: 10 250 m
Mass: roughly 470 000 000 kg
Total block count: 940 000 (estimated)
Number of sections: 20
Section length: 512.5 m (205 blocks)
Section width: 250 m (100 blocks)

This took more than 40 hours to make

I'm not very pleased with it though. It is too elliptical, the mouintains looks odd, I'm not very happy about the biome distribution, and the savannah biome looks terrible.
It was originally supposed to have fewer, but larger sections. The sections would also have walls and a roof of window blocks, fully pressurized and with airlocks at the joints. This (of course) was far too heavy on performance.

________________________________________________________________________________

I've seen a lot of arguing in the comments wether or not this is from Halo, and I feel like I need to make a comment on this.

I don't really know for sure what a halo ring is, besides a ring-shaped planet-like megastructure. I've never played any of the games in the halo series.
This was mainly inspired by the ringworld, which I first learned of from stellaris. I obviously couldn't make one large enough to be classified as an actual ringworld, so its more of a ring-shaped habitat station: a space station built to serve as land to build houses on or as a wildlife preserve. So in conclusion: technically it is neither a ringworld nor a halo ring, but it can be either of them if you want it to I guess.

The reason I haven't made this clear until now is because I found the arguing in the comments to be way too entertaining.
Also, it seemed like people prefered to argue rather than just asking me.