https://www.lowes.com/pl/Radiator-covers-Heating-cooling/4294395587 Here are some at Lowes. If you really want to make them, then maybe go look at these and get some good ideas of what you would like.

I think it depends on the style ofthe house. If you are maintaining the original look of everything else, I'd sand blast them and have repainted by a vehicle body professional...

if it's a funky interior, I'd build wooden replacements with a screen front to create your own style. How many are there? and can you create/incorporate something useful in a custom build? I'd like to see the whole room and placement.

Some older homes doln't have covers. Some people actually search out old radiators because they like the vintage look.

https://www.houzz.com/photos/query/radiator-cover/nqrwns

 the apartment You Don't Own and you can't do anything to it without talking to the landlord

As someone said, auto body shops do sandblasting. I had this done to flat metal floor vents (I think there were 8 or so) about 10 years ago and was very very pleased with the results. I think the whole job was $40. But I live in a very rural area, this was 10 years ago, and my floor grates were a lot smaller than your radiator covers.

These are very specific style of radiator from the 40s and i am assuming under a window. we had them in a previous rental. the hot water is going through a pipe in the wall just under those vents you see and has several fins on it. cool air is drawn in under through the bottom throught the fins and out the vents at the top. The metal cover also gets hot and also heats the room. be very careful if you build anything to not disrupt this flow or you will lose its effectiveness. there should also be chains attached to each to lower a flap at the bottom to stop the air flowing up. i would clean off or sand the paint (test for lead) and repaint them. a cover is strongly not suggested because it will stop this air flow system. and i would remove the metal covers every fall and vacuum them.

We are assuming this is your own home since either replacing or renovating these covers is costly and time consuming. There are a lot of radiator websites (I had an old home once and had to look for covers) and they vary in price quite a bit. Take one cover to a metal repainting place to find out the cost of sandblasting and repainting them. That is usually the best solution. Correct size is important with these.

Hey happyleg, I own my apartment. It's a 2br 1ba duplex fixer upper. But thanks for the concern! Have a blessed day.

If you were to make something for it in a design of wood you going to be able to have to maintain it so it will probably have to pull away from the wall it probably shouldn't be anchored and you can make the wood in style like slanted wood or herringbone Style

Thanks for the feedback everyone! For the most part, i'm ok with the style of the cover and don't necessarily want to spend money on swapping out when I don't have to, i just want to make them look nicer. So far, I've only opened and vacuumed the insides, and even though they're a bit rusty, they *are* functional, so it's just a cosmetic problem for me. However, I've never actually seen any of these covers that have never been painted over, so I'm not exactly sure what "look" I'm trying to accomplish with them. Sounds like sandblasting is not as expensive as I was thinking, so maybe doing that and starting with a fresh palatte will help. I'll see if I can find a place to do the sandblasting in the tri-state area. 

Also, thanks so much Stephanie for explaining the design. I've seen similar radiator covers in pre-war buildings in NYC and was aware the design had something to do with directing the airflow, but your explanation clarifies it much more. The ones in my apt are all under windows and the inside radiator is exactly how you describe. Only difference is that the top vents are not adjustable, they only face upwards.

Ditto the suggestion re: asking auto body shops about sandblasting. They will give you a better price IF you can leave them until they have another bigger job to do. I strongly suggest you find a "double-walled" corrugated box to hold them, nest them carefully so they don't get bent out of shape. After that, take them in to be painted using the "powder coated" method so they will never rust - the body shop can refer you. Carefully and gently wipe the "interior fins" to remove any smoke residue, check the chains for ease of movement and replace parts if needed. Local, small hardware shops are invaluable for parts and advice when you buy in an old building...remember this advice when you have a plumbing issue.

IMO take all the covers off and clean out the mess for sure it will probaly lower your heating bill dramatically . yes thre are great options we have how wanter heating with baseboard rads and got new covers from HD and they are awesome