To add to Brians pretty exhaustive list of magazine articles are three relevant books. All cover U.S. prototypes and their modelling, though, as the laws of metallurgy are common on both sides of the pond, so is the equipment (railways aside).
Firstly, Dean Freytag's, Â 'The History, Making and Modeling of Steel', originally published by Walthers as part of their steel mill series, it was long out of print and was going for silly money. The NMRA managed to get Walters to re-print it, currently on special offer at Walthers;
http://www.walthers.com/exec/productinfo/98-20
A large hardback, it is mainly devoted to the prototype with a bit at the back about using Walthers kits.
Secondly, Dean Freytag's, 'The Cyclopedia of Industrial Modeling'
Pure plastic modelling, not entirely devoted to steel but relevant to any industrial modelling.
http://www.hobbylinc.com/htm/pls/pls115.htm
and finally, Bernard Kempinski's,  'The Model Railroader’s Guide to Steel Mills'
http://www.kalmbachstore.com/12435.html
in Kalmbachs typical softback style, similar to Deans first book but with a little more modelling though not what you could call a step by step approach.
Arthur