Based on the book, maybe a little something along the lines of this, but without any living greenery. 

What's important to me: Ruins. Dying sun. Dying world (no wind, nothing alive, nothing). Hall of "wax" figures should be properly creepy. Plus bell. 

But the specific look of everything and everyone is open to interpretation. Obviously we've seen that they've chosen to do kind of a 50s sci-fi look for Jadis which is a different choice than anyone expected. I think we will see a similar look for the world-building. Something like this maybe? Or this? Or this? (But without any artificial lights or robots.) 

A sci-fi world is not how I personally pictured Charn, HOWEVER, there's that bit at the end of MN where Aslan takes Digory and Polly to the Wood Between the Worlds, shows them the dried up puddle of Charn, and warns them that that could happen to Earth. So I don't think it's too much of a stretch to show some kind of futuristic world that's well past our technological understanding, but has gone rotten to the core, so what good is all that stuff?

Sorry, I went a bit off-topic there @DavidD, but I am SOOO curious to see how Charn is imagined for this film, particularly with Jadis's get-up. 

ETA: Also DavidD, I really love your picture 7. Is that one of your creations?

The book description always felt fairly conventionally medieval to me - stone columns,  big heavy wooden doors, lots of pointy arches. 

If there was any element of a sci-fi twist it would be more along the lines of say an old Star Trek Original Series episode where they'd find an old planet which resembled a quasi-historical approximation of real history 

That's the Planet Vulcan I believe 

Posted by: @fantasia

ETA: Also DavidD, I really love your picture 7. Is that one of your creations?

No - the image was from a wraparound design for mugs, phones and stuff published by 'Alexi does Art' see Alexi Does Art merchandise. (Is Alexi a person or a company?)

The only images I generated of Charn were poor attempts to reproduce Pauline Baynes' style

E.g. Charn courtyard & Digory & Polly in Charn

The pictures below are how I see Charn, or at least the walls inside the palace. The first one is obviously from an Ancient Egyptian display, but the second one was from the Assyrian ruins examined by Austen Henry Layard. I saw similar murals in the British Museum, where there are quite a few displays there of how Assyrian kings conducted battles & lived their lives. The nearest link @davidd listed to how I imagine Charn is Charn 5, where there is a picture at the right of where Jadis is standing, facing Polly & Digory. 

This is how Ashurnasirpal II (r. 884-859 BCE) recorded the way he had dealt with his enemies during one of his military campaigns. I could well imagine the later kings in the Hall of images similarly decorating Charn's palace walls with their deeds. 

This sort of thing, whether Egypt, Assyria or elsewhere, gives an idea about how Jadis' world really might look like, in my opinion. But tapestries etc, can suggest the same thing in that St Bartholomew's church, maybe. 

When I first had the book read to me, the image I saw when Charn was described was this one or at least the pen and ink original.  To me, the buildings in this image look European and 20th century. As I reflect on how I imagine Charn, I think I really picture it as a 1945/1946 European bombed out city (Warsaw, Dresden, Berlin or the bombed out parts of London come to mind).

The differences (in my mind) are the bricks would be large stones (more like medieval buildings), and no glass, electric wires, metal gutters to be seen anywhere.  The windows and doors would be arched (kind of like Roman arches) and there are a lot more pillars.

But essentially, I picture Charn as a war-torn city echoing our world's post-war cites of the late 1940s. 

Posted by: @davidd

But essentially, I picture Charn as a war-torn city echoing our world's post-war cites of the late 1940s. 

I agree with this although I don't know if the buildings would be bombed to begin with or would that come after as an effect of Digory ringing the bell (if my memory is correct there is a lot of rubble and a falling wall as they leave the Hall of Images)? I also took the red sun description quite literally and imagined it being bathed in a red glow (similar to the Planet Vulcan images shared by @icarus ). 

@moonlit_centaur 

Yes, agreed. I did not mean that Charn had been bombed. Just that its ruins and rubble have a similar look to those bombed cities. C. S. Lewis comments on there being rubble around before the bell is struck, but it is after the bell is struck that the walls collapse at the far end of the hall of images (and as they escape with Jadis, they hear rumblings sometimes close by, an arch collapses just after they went under it). The impression I got was that the bell’s sound caused more destruction than had happened for some time).

@davidd Just that its ruins and rubble have a similar look to those bombed cities 

Yes, Pauline Baynes' illustrations for the Narnia series are really hard to beat. I was watching a You Tube discussion about Sennacherib's siege of Lachish in 701 BCE, one of the most documented Biblical events, ever, when Sennacherib's own scribes also wrote about this siege, on hexagonal-ended cylinders still extant, their efforts have also been consulted, and when these wall panels below, from the British Museum, are also a description of what happened.

Now, back then, they didn't have bombs around, but war-torn ruins from way back to the Assyrian Empire are still around, or at least Lachish, apparently, though the Assyrians famously didn't manage to do the same to Jerusalem. The series of You Tube programs done by a Christian archaeologist, did mention Jerusalem's own siege of 70 AD (or CE). The archaeologist and his interviewer were sitting on a pile of rubble, near where Herod's temple was situated, when the interviewer asked what evidence there was for the Roman siege. The archaeologist replied that the interviewer was sitting on it, one of the more enjoyable moments in such programs. I've also been to Troy, near Cannukale, in Türkiye, but mostly it is trenches, with nothing much to see, after so many millennia & centuries. 

Charn 3 in DavidD's original post is similar to how I envision Minas Tirith from Lord of the Rings (with its seven leveled structure).

@starlit

Ha ha, Now that you mention it, I can see that - though to be honest it gave me the “tower of babel’ vibes (at least as traditionally depicted in art - I know scholars think the tower was most likely similar to a Ziggurat / Pyramid, but that’s not how it’s depicted in art work).