Designing layouts has many different approaches.  Mine was I had a space 20 x 50 ft that was built for a model railroad HO and how was I going to fit RR into the space.  First the overall design I had seen some were else.  But I had more space and plans for a lot more staging. 

In this picture you are looking at Silverville on left and Rock Ridge on Right.

Objectives, longest possible main line, no reach to industry more than 30", no aisle less than 4.5 ft. Your train visitable to you as much as possible. Long sidings to be able to run long trains. This is operating layout have no interest in off line structures.  12 men needed to fit in and pass each other. 

I drew up plans for bench work and main on graft paper first.  Put bench work in and than took butcher paper covered the bench work and started placing main sidings and industries.  If I did not like it put new paper down. This was a lot quicker than me learning the CAD system and putting it into service. Bough one still in the box.  I also marked were the plywood cut would be so their was no dough that what I wanted would fit.

This video will give you a look at the out come and though that went into Rock Ridge.