Joe
Sorry to sort of hijack your thread. Back to your concern - with this much space, $$, and time that you will invest, you need to be as clear as you can be on what you want to accomplish. The better you can define your vision, the happier you be over the long term with the result. Some examples:
1) You mention 2 ft wide shelves around 3 sides of the space that is 12ft wide. The 12 ft width leaves room for peninsulas to increase the size and running length of the layout. Are you interested, or do you just want the shelves? A 2ft wide shelf is not really enough to turn around in any scales except N or Z - and even N would be limited. This will restrict you to point-to-point. Are you willing to give up continuous running? If you wanted it, continuous running in HO and larger scales is most easily accomplished with the aforementioned peninsulas. In N, you could get away with widening the shelf to 30-36 inches.
2) You didn't mention a scale or gauge. Model Shays are readily available in G, O, On3, On30, HO, HOn3, HOn30, and N - although some are more expensive than others! I'm sure there are brass Shays in S and/or Sn3.
3) Era and locale may or may not be a major influence. Most logging models are modeled after prototypes built or operating in the 1920s to 1930s. If you are after an earlier era, On30/HO/HOn3 have the largest availability of commercial items - and even then it will be limited. Logging rail operations in the Pacific Northwest were quite different from the South in terms of equipment used (loaders, etc) and the scenery.
4) Particular scenes and structures that you want to model have a major impact on layout design. Do you want an incline section (where loaded cars are lowered by winches, capstans, and ropes)? Do you want a log flume, a large sawmill, a log pond, or none of the above? Will your logs be herded and loaded by spar tree, steam donkey, oxen teams, or the manufactured loaders? Same for the mines - are there particular mine structures you want to build? What kind of setting and space do they need? What kind of ore cars do you intend to use? How heavy is the ore?
Another way to get at your desires is to examine layouts, layout plans, and your reaction to them. What did you like, and not like, about a given layout or track plan? In the 1960s Model Railroader published an article about a layout called "Bullfrog Logging Co" (I believe, will check my back issues when I get a chance). It was a very simple point-to-point logging operation using Shays around 3 walls of a room. It was either HO or HOn3, and featured a very simple terminal with small turntable at each end. There was an incline in the middle section, and the main had 5% grades. Don't remember much else - my age is showing. Might have been in the same issue that had multiple articles on rail logging operations.
Hope this helps