With a 5 by 8, I'd say do tidmouth sheds and yard., have a 2-3 mainline oval with the shed and yards at one end and add a good stretch of mainline for a more country view. I'd say give 3 about 8ths of the layout to that and 2 8ths to the main line part.... just a quick idea, I didn't mention certain areas cause I figure your mind can start wondering and figure ideas out to fill in the gaps I left.