By "simple metal buildings", if you mean pre-engineered metal buildings, the design information is proprietary and not published for the public's use. The base the design on building codes, but they don't publish anything that I know of.
Einsteim is right. Those guys keep their secrets as secret as possible because they pay gazillions per year on research and development--something that most EORs don't have to do (massive R&D makes no sense in their line of work).
However, it's mostly AISC and AISI steel design, just going WAY beyond compact hot-rolled members, etc. that EOR-types usually use. The use of built-up members and automated fabrication allows them to do things like taper the frame members, change plate thicknesses many times, etc., to get optimum designs. Also, for example, rather than over-designing a connection for speed, they'll pull out all the stops and use yield line analysis, etc. to get the optimum plate thickness. There's really no magic to it, just very rigorous calcs that don't make any sense to do for conventional bldgs.
The roof and wall panels are a major area of secrecy because they develop and roll their own sections, pay big bucks to have them tested and approved for uplift, etc.
If the main issue is how to design tapered members, be on the lookout for the MBMA/AISC tapered member design guide which, to my knowledge, isn't out yet. It will be the authoritative source very soon, and will have lots of examples.
