Quoted from JodyG:The cool thing about Lego, is that if you do the first one well and it sells... Next you can do a Castle theme, City, Star Wars, etc. Tons of opportunities with that franchise, and a quite broad appeal.
Make a component out of Lego Bricks and give the buyer the option to build several different variations or layouts from the same parts the way the kits do. Opens one "theme" up to a larger audience.