Much like the sketchup approach i use autocad for my SCX digital designs. It is easy for me to use since i am a building engineer and now the program well. It gives me great freedom to build a layout and also make sure it will fit in my livingroom.
I drew all the trackpieces i have in 3d (not a completed project yet) and can easily build behind my computer.. it takes some time but it is completely hassle free.
If anyone would like the .dwg file witch the track pieces just let me know, i will be happy to share.
See my 2 examples wich will barely fit in my house

(also i would appreciate some input on my track designs)