Have you read the books on the subject in the public library yet ?,
that can include current and back issues of magazines..

I haven't found anything current. I bought How to Specify Your Bike: A methodical approach to all the decisions for buying or building the right bicycle by Dave Peart, and it's over my head.

I know you were asking about frames to build up--but thought I'd throw this out there for ya. Pure Cycles has reasonably priced steel framed bikes--you can buy them unassembled or assembled. Might be just about as inexpensive to buy the whole bike (plus you know all the parts will go together). Here's the link> https://www.purecycles.com/collections/bicycles

Why do you trust external links more than what people on here might tell you?

If you're going to ignore everything except for hyperlinks, use Google, not a forum.

Learning about bikes by buying a frame and parts seems totally backwards to me. Probably learn more and save a considerable amount by picking up something used and rebuilding it/fixing it up. When you're done ride it for a while and figure out what you like and dislike about it. Then you'll have a much better idea of what your needs are and start shopping around. The bike you fix up can be sold (don't expect a profit) to fund the new bike.

Fairdalebikes.com. I got one for my son a year ago and it has been fantastic. Two other guys at the shop picked up frame sets and really like them. Only steel frames, good quality, priced from 460 to 2500. My son has the Weekender Nomad. Mildly expensive model, but a wonderful ride. He commutes, gravel rides, and brevets with it. Fairdale designs their frames from a BMX background and are over built for sure, but are strong!
The Fairdale Archer is under $900 and is full 4130 cromo. Of course they don't use the super thin walled stuff as it may not be durable enough from where they stand.
The Fairdale design is stable and very predictable with or without a load. They are not super light, but again super light does not fit the design parameter for durability. Sealed cartridge bearings in the hubs and bottom bracket. Super low maintenance. SRAM X5 is mid grade stuff and works well. 9 speed drive train, single chain ring

+1 wide tires=comfort. Well, wide "supple" tires. On my stiff, steel Nishiki Blazer Mountain bike I am coming a summer riding light, supple 26x1.85 WTB slicks, and just put my heavy, stiff 26x1.65 studded snow tires and what a difference in ride comfort! The big, fat slicks were so fast and comfortable, they just didn't feel fast. Yes it's steel, but the Blazer frame is stiff and solid.

As far as steel being more comfortable, all three of my bikes are steel and there's a difference in stiffness. My 1983 Nishiki International roadbike is very light, and very flexible. The seat stays and dropouts are thinner and more flexible than anything you see nowadays. With stiff 700x23s you really feel the flex, but it still beat me up, so I put 700x32s on, which wou;d only fit under the fork crown if slightly under inflated. That was very comfortable, but I was less aware of the flex (although I'm sure it was there). Lately I've been tiding 700x28s which are a happy medium. I can feel the frame flex and the wheels aren't punching me.

My main commuter is a 2015 Charge Plug. (It's steel but for 2016-2017(?) they're aluminum, but now they're steel again.) It is the perfect blend of my other two bikes. There's a little flex in the frame, but the big difference I feel is tires. I've run 700x35 to 700x38s. Stiff, heavy 700x38 Continental Touring II's had soft, sticky tread, but the sidewalls were stiff, making for a harsh ride, although the frame helped a little. Currently I'm running light, cheap, supple Metro brand tires, and it is the most comfortable it's ever been.

While I think the old, curved, thin tapered front fork of my old Nishiki International helps with comfort, you aren't going to find a modern disk-brake bike with that. And from what I read, even some straight, carbon forks provide some nice flex, straight steel doesn't.

Bottom line...I subscribe to what Jan Heine from Bicycle Quarterly maintains...that softer sidewalls provide a more comfortable, and faster ride...that has been my experience.

My advice to [MENTION=491269]galapogosian[/MENTION] is to buy an old, light, skinny, steel frame bike that fits (like my 1983 Nishiki International) and resto-mod it with newer parts, like brifters and a newer drivetrain. Forget disk brakes and keep the slender, curved front fork, mount some light, supple tires, then ride, ride, ride!

Waybac ... Pro frames of steel , famous names , shipped to retail shops assuming dealer did the frame prep,
and needed them to have the tools for final cutting of BB threads and facing & reaming headtube, etc..

some economic sense; tool wear spread out around the globe, rather than doing it all in one spot..
and good prep, with cutting tools, is best if not hurried..


Now, many companies go to OEM factories, that produce multiple brands
out of the same place.

Maxway Ltd TW, is one of those OEM multi brand companies ,
specializing in steel ..




...

Here is one list ... a place to start. Many of the makers offer framesets instead of just complete bikes. Many of these are steel frames.

2018 Touring Bicycle Buyer's Guide @ CyclingAbout.

Although she has stopped writing new articles, the most useful link is lovelybike.blogspot.com. You will discover that British frames (think Raleigh DL1) are different than Italian frames (of which the Bella Ciao, frame made in Italy, bike assembled in Berlin to German standard, is her favourite), with different performing frames from Sweden, Denmark, Germany, France, and more recently Asia. You will learn about front fork angle where one design is for sport and another angle gives comfort. You will learn about saddles where the 100-year old design of the Brooks leather saddle remains king. Discussion on tyres... thin, thick, fat, large diameter vs small, tread and even colour (she prefers cream). Then, if you read her site by date, you will discover how she began as a novice wanting to give up a car and use a bike to get around Boston... a city bike for all seasons. Then she begins to meet bike people and go on rides, competitions and you enter a subculture of biking where words like randonneur surface

To briefly summarise, the Randonneur is a lugged steel low-trail bicycle with 650Bx42mm tires, fenders, dynamo lighting, front and rear racks, and a handlebar bag - made in the style of the 20th century French constructeurs. "Low-trail" refers to the front-end geometry of a bicycle and it differs from the typical mid/high trail geometry of most roadbikes today. Among classic and vintage bicycle enthusiasts, there is definitely a mystique surrounding the low trail randonneur, and dramatic descriptions of its handling abound - made all the more dramatic, I suspect, by the fact that this type of bicycle is fairly rare and few have actually ridden it.

As you can see, you no longer are limited to the entry conversation about steel vs aluminium. Steel is presumed because it bends, whereas aluminium must be rigid or it breaks... which means shock absorbers instead of shock absorbing steel by how the front forks are bent.

After reading her articles, we flew to Berlin and bought two Bella Ciao bicycles that we rode all over Berlin, then Dresden and then back to the airport in Prague where we boxed them and shipped them home. Back in the land of hills, we promptly removed the cranks and bottom brackets and added Bafang BBS01 electric mid-mount motors with 36V lithium ion batteries, converting them to ebikes where they have become a primary form of transport for us.

But, we did find that if we load the bikes up, the Italian frame becomes too whippy; thus we had to acquire other bikes with stronger frames built for hauling. THe questions as to intended use become relevant. In cars, we own a 2-seater SLK for good weather coffee runs, a gas guzzling G-wagon when we need to pick up six people at the ferry or haul a ton of rocks, and a Toyota Ractis to go food shopping on the least amount of fuel when the weather is too foul to bike.

If you're commute is fairly flat, Wabi single speed bikes are a solid option: https://wabicycles.com/