Layout design software: what it is and is NOT
Layout design software is useful for:
- keeping turnouts to reasonable frog angles
- making sure you don't draw a "kink" into the track
- allowing space for easements
- making a 3D visualization of what it will look like
- double checking track for side to side and overhead clearances
If you get good enough at a software package you may find you can doodle track plans faster on the computer than by hand.
But, no layout design package out there will "design" your layout for you. They will not tell you about an imbalance in the number of staging tracks vs number and length of yard tracks vs car spots at industries. (NOTE added by Joe Fugate: If you want insight on these kinds of issues, here's some handy layout design analysis formulas.)
They won't tell you that your planned operating scenario just plain won't map very well onto the trackage you've planned.
And for the most part trying to run trains on the computer to validate an ops plan is mostly a gimmick/waste of time.
The software packages are basically smart pencils.
If you'd design a lousy plan using pencil and Armstrong squares you'll design a lousy plan with a CAD package. If you'd design a brilliant plan manually, you'll design a brilliant plan with CAD assist.
The computers are also good at giving precise information about benchwork widths and where to locate the center of a curve.
I've found 3rdPlanit to be very useful over the years. I've designed 2 layouts with it (plus some modules. I've designed a house and use it as a general purpose cad package for things like string diagrams for scheduling trains or 3D illustrations and diagrams).
I typically no longer try to design a railroad down to a gnat's eyelash. Instead I just use it to make sure that what I want to do with a space will fit (with a little slop).
I find that often, as I'm building the physical layout I have other ideas regarding laying out trackwork and I'll incorporate those changes as I build (sometimes going back and putting them into the 3rd Planit file).
I've used 3rd Planit to tell me the lengths of a series of joists projecting from the wall when the fascia has some curve to it and also to give railhead heights when curvy track is on a grade.
One final question: How much experience do you have with layout design, construction, and operation? If the answer is "not a whole lot" I'd strongly suggest NOT embarking on a "dream" layout. Because as your interests, skills and knowledge change you likely won't think of your basement monster as a "dream".