Since a 4x8 takes up the same amount of space as a 6x10 because of the need for access to all four sides, you may want to consider something a little different. This layout has had a little discussion on here lately and just might be a good starter.
If you have the room I think this would be a much better and still easy and economical alternative. Still uses only one 4x8 sheet of plywood but has a lot better design than the standard small "spaghetti bowl". Also allows the trains a bit of space to run.
"N", the Normal scale!