A few items that I have
A few items that I have researched quite a bit, and are somewhat ingrained in my thoughts at this time.
Height of the dbl-decks:
I am a tall person (6'4") and still very healthy. I have experimented with various heights of sitting and standing, and have read a number of different accounts of different layouts. At this moment I am stuck on the idea that the lower deck's 'working surface' will be 40" off the floor. Possible I would consider 1 or 2 inches lower.
The upper deck will be 20" higher...60" inches from the floor. I imagine that the depth of the upper deck will be considerable less than the lower deck to allow for best viewing, and to allow for moving myself around even with minimal isles, 22 to 24 inches. It has been suggested that I might consider not putting an upper deck over the peninsula area (at least in the extended head of the peninsula). I will take that into consideration.
Helix
I have debated this question to some great extent, and done quite a bit of reading about it. I am not excited about the gradual rise of an around the wall grade. It would take up that much additional width that I do not care to give up in my relatively narrow shed. In fact I even considered not insulating the shed and thus being able to build some portions of the layout into the 2x4 studded areas, but the better part of valor said I will need AC at various times here in warm humid FL.
I am not married to the idea that my trains need to make constant use of this exchange between levels. With that in mind I am only considering a single-track helix, unless someone can convinced me otherwise. Trains will have to wait their turn to use the single trackage...not unusual?
And someone commented about 'how about when it is raining' on my 'external helix'. First off when its raining perhaps I will have NO traffic on the helix,...just run my multiple trains on the lower level, and a single freight/passenger train on the upper level, and perhaps concurrently my logging train(s) on that mountainous area in the upper level (isolated from the mainline) there.
I'm imagining the donut shaped helix housed inside a short flat box like structure built of square tube aluminum tubes that can be bolted up to rear external face of my metal shed (to the studs of the shed), and with two 'legs' at its outer edges. I will be able to access the inner hollow of the helix from up underneath. Naturally the box structure that houses the helix will have metal sheeting covering it just like the shed itself. I have all of this alum metal already, and chose to utilize light weight alum rather than heavier and rot prone wood-frame construction.
I am imagining that the lower entrance to the helix will be from a track that is already rising in grade from the blob/head portion of peninsula (in order to pass over other tracks at the root of the peninsula)....so one less level required of the helix itself. It will then rise up to the upper level and enter back into the layout room in a straight shot down the long edge of the shed/layout.
Foam Subroadbed
Lots of reading again, and I have become convinced of the many virtues of foam subrodbed. I had some doubts as to constructing many grades with foam construction, particularly as I used to have a cookie-cutter layout with many wood risers. But as I look at it greater depth I see many advantages of foam construction.
I will use 2” thick foam for the basic shelfs of the layout. I am seriously thinking of bonding a piece of 1/8 Masonite onto the bottom of this 2” foam. With proper gluing it should just add to the stiffness of the subroadbed when it spans the 24 inch wide shelf brackets attached to the 2x4 studding of the shed walls. It is my understanding that this will also cut down on the noise generated by the bare foam. And it will provide good mounting surfaces on the underside of the subroadbed.
There are a number of reasons to chose foam, but another compelling one in my case is twofold. I want minimal 'thickness' in my framing for the subroadbed, Obviously it means one does not have to provide as great of a distance between the top and bottom levels of the dbl-deck layout (for proper viewing, nor for the total rise of the helix). But I also wanted this minimal thickness for my bottom deck,...why? So I could provide for some staging tracks down under the bottom deck without have them very far down in height. I intend to utilize some of those welded steel shelf brackets that do not protrude down into the immediate area under the subroadbed, like even the stamped steel ones do.
Work Bench & Tools
I am going to try my best not to have space inside the shed devoted to work benches or power tools. I hope to have those outside in their own little covered area
Scale & Track Radius
I saw this questioned posed. The scale is HO.
I'm hoping to limit my radius of track to 24 inches, except of course in the logging areas
Prototypes & Operations
To answer your questions Don, I am not real concerned about prototypes, nor operations. Nor am I a rivet counter. I like to see trains running pass industrial sites, etc. I do have in mind a nice little harbor scene where some operations might be appropriate,...and in the logging scenes, and in the freight yards.
Backdrops
I'm putting up Masonite to cover the insulation I put in between the studs and in the ceiling. I plan on initially painting this some sort of sky blue with clouds. (I also saw a rather neat idea of some hanging 'cotton clouds')
I have a lady here in the park who is suppose to be quite an artist, and who has volunteered to paint some backdrops. Since her 'mobility' is somewhat limited I thought I would have her paint those backdrops onto some sort of 'paper material' that I could then glue to the Masonite backdrop.