If you were a fan of Dwarven Forge, UpWorks is from the same guys.
From the campaign:
For decades fantasy enthusiasts have dreamed of a modular castle building system that would allow them to quickly create beautiful customized structures. Who hasn't dreamed of building a massive wizards' school, a gigantic castle wall to repulse invading goblins, or a ruined castle leveled by dragonfire?
UpWorks utilizes a simple but amazing patent-pending floor frame system which gives you the power to swiftly create towers and castles - and then easily move them around by levels as needed. The pieces are quickly secured to the floor frames, so your creations go up swiftly and then stay up until the fun is over.