I've been thinking about this lately since I've been heavily focused on designing a layout for my next project. I've found that usually I start my layout as a top-down sketch on paper, but I can never really take it very far on paper because scale, distances, and elevation changes make it hard for things to work in-game like I thought they would on paper. Because of this, the bulk of my layout design has been happening in Hammer with large blocks and temporary corridors until I get what feels to be a good layout. I don't mind doing it this way, except that I realize how much more time it takes thanks to compiling, trial, and error. On paper an eraser would do the trick much faster. Does anybody else do it like this? Or are some of you able to take the design process pretty far on paper?