Here's my idea! Make multi-add ons that can be pieced together on any size plot or compliment any house design to make a really cool looking castle; gatehouses, battlements, walls, wells, balconies, gardyloos, towers of different sizes, textures, shapes, new gardens, gypsy wagon, stable, armories, etc. Stuff that we can't build right now, like round towers that look good, wagons, etc. that could be an add on.
If they had creative features that would be wonderful, bonuses, extra storage, etc. I think we'd all like that and it would go with the new stone masonry items that have already been implemented successfully in game.