Hi Eric,
For basic sheeting I use 1/16 and 1/8" for the base model, and use .01, .02, and .03" for panel detail, and larger detail work such as hatches. I picked up a 4’ x 8’ sheet of the 1/16 and 1/8 from a local plastic producer for $100 CDN. After 10 years, I think I still have about half of it.
For the tops of the open cars, I use 24" lengths of .188 x .188. ( Evergreen 398 ) I just imported 10 packs from Australia as the Canadian Evergreen supplier no longer stocks them.
Car ribs are normally 1/8 (.125) from .02 to .5.
End framing is made up with .125 x .04 and .100 x .03 glued into an angular piece. It seems to give me pretty good strength.
.05" round for ladder rungs.
.04" hex for bolt detail.
If you watch my photo compilation videos, I try to photograph each step with the package of styrene I am using for whatever part I am working on.
Brass stirrups on the rotary gons are 1/32 x 3/32 flat bar.
Hope this helps.
Shane