Reddit reviews Techniques Of Medieval Armour Reproduction: The 14th Century

So these are really dependant on a ton of factors. Material, size, style, era, etc., so to get exact weight ranges, you're going to want more information.

However, Wizards does provide tables for this sort of thing. The SRD also has a table here: https://www.dandwiki.com/wiki/5e_SRD:Armor

You may want to investigate some historical armour texts also: https://www.amazon.com/dp/1581605366/ref=cm_sw_r_cp_apa_i_tR9NDbT79Y7M4

Ok, in addition to the paper/booklet posted earlier from acedemia.edu about the lorica segmentata here are some other resources discussing armor and some on metal work techniques. Much of what is available is medieval period but many of the skills and techniques are similar.
On Divers Arts by Theophilus is a treatise on painting, glass making, and metalwork from roughly 1122ad. ISBN:978-0486237848

De Re Metalica by Georgius Agricola is a scientific book on mining and metallurgy from around 1556ad. ISBN: 978-0486600062

The Pirotechnia of Vannoccio Biringuccio is a treatise on metallurgy and alchemy/chemistry from 1540ad. ISBN:978-0486261348

Techniques of Medieval Armor Reproduction: The Fourteenth Century is an awesome book covering various metalwork techniques as applied to making 14th century armor. ISBN: 978-1581605365 He talks about tools you will need and some modifications to make to them for ease of use. He even gives you some ideas on finding good sources for drawing inspiration from for your armor patterns. If you are starting with making armor and don't have anyone nearby to help you learn this is a good guide to buy.

Best of the Hammer is a black and white series of booklets that have great info on medieval metalwork from chainmail to bladesmithing. ISBN:978-0943228044

Roman Body Armor, by Hilary & John Travis is a good re-examining of the data on Roman armor up until this point. ISBN: 978-1445608037

Armorer here. Not sure of your skill level, but Brian Price's Techniques Of Medieval Armour Reproduction is a required text for any armorer.

The Armour Archive is also a terrific resource for pretty much everything armor related with tons of very experienced folks that can answer pretty much any question you may have.

What are you looking to make?

https://www.amazon.com/Techniques-Medieval-Armour-Reproduction-Century/dp/1581605366

This has everything you'd need, if you're willing to read it and not skim.

Here are 2 resources that may be of help...
Armourarchive and [this book] (http://www.amazon.com/Techniques-Medieval-Armour-Reproduction-Century/dp/1581605366/ref=sr_1_1?s=books&ie=UTF8&qid=1415593510&sr=1-1&keywords=medieval+armor)

For the OP, there were ways of making steel into sheets or at least plates in the later middle ages and early modern period: water-powered trip hammers. You can see an early modern in action shaping a billet of steel in Sweden here and can see a fairly realistic rendering in the background of this very allegorical painting of Venus visiting the forge of Vulcan asking him to forge the armour of Aeneas. It may have been used for rough shaping by actual armourers, but it could also (and perhaps more importantly) be used to flatten blooms of steel or iron into plates that were more easily worked. By contrast, rolling steel is a 17th century process, more or less, and so was not used for most of the period that plate armour was used.

I'm going to answer this separately since it's actually a bit different than the question in the OP. If you're talking about a historical method of making armour finished that doesn't involve some combination of cold and hot work with a hammer, no, there isn't any good evidence for such a process being used historically, at least none I've seen that's convincing. The only alternative I can think of to hammering out plate armour is stamping it using a kind of dye, which is both much more coplex from your perspective and something that I have yet to see evidence for. Probably the best writing I've seen on the historical methods of armourers at the forge is the Phd Thesis of Nickolas Dupras, which analyzed tool inventories, other written accounts and most importantly the actual hammer marks on surviving armours to try to determine working methods. In no examples that he analyzed were there any signs that the metal was shaped by anything other than a hammer. Now, in his Phd Thesis Matthias Goll did argue for some kind of water-powered stamping mechanism, but the argument he presents for this is tenuous, involving the similarities of surviving pieces (it's possible that some armours were hammered on forms that would contain the basic shape of say, a breastplate but that is different), a rather strained reading of an allegorical biography of Maximilian I and little else that I can recall, though it has been some time since I read the thesis.

Regarding the last part, the laborious work of polishing? That's also inevitable, unless you want to make an armour 'rough from the hammer'. Historians like Tobias Capwell estimate that polishing was the majority of labor hours in producing plate armour, and then as now armourers tried to use labor saving devices like polishing wheels powered by water (at least by circa 1500).

Fortunately for you if you are simply seeking to make armour most modern armourers seem to take advantages of alternative means of heating steel like various gas torches, so your ability to forge something in this day and age isn't restricted by the size of your actual forge. There are a number of books and how-tos on making armour, many of them not very good and pretty much all of them more about creating the right look than using the right methods. However the best of the lot is still probably Techniques of Medieval Armour Reproduction: The Fourteenth Century. You may want to try to do things 'the real way' and that's admirable but frankly it's very difficult to do it in this day and age - raw materials are too different and moreover the whole way armourers work has changed due to changes in the labor market. Modern armourers are solitary artisans that do all steps themselves. By contrast medieval and early modern armourers were working in workshops with multiple people - at least a couple or a handful, but as many as dozens, and they were working in a larger community of artisans that could allow for division of labor and economies of scale. This made shaping steel, finishing it and polishing it all using hand or water-powered tools and (char)coal fired forges for heat more feasible than it is for a single person working in their backyard, garage or shed today. That larger social context is something we need to think about whenever we think about reconstructing objects from the past or trying to learn about historical methods of craft through practicing our trades in the modern day.

Caveat: I am not an armourer.

Greenleaf workshop on YouTube does some very nice tutorials, a book that comes to mind is Techniquies of Medieval Armour Reproduction: The 14th Century" by Brian Price (https://www.amazon.com/Techniques-Medieval-Armour-Reproduction-Century/dp/1581605366). I haven't read it myself, but I understand that it is very informative.