There is a Computer Program (free I believe) called "Easy Shop Designer" that I found that allows you to do a shed/workshop layout. Go to http://www.inthewoodshop.org/software/software.shtml

Another one is at ToolDock (US Company with nice modular tool benches = expensive though) "Design Your Shop" using a web based flash app. Go to http://www.tooldock.com/designyourshop.asp