Here are a set of rules for a tower defense game with miniatures.
The premise, according to the author:
You are the sole defender of a precious Portal which allows travel between worlds. Orcs want to travel to other worlds, because theirs sucks. They will smash down the gates and doggedly pour through the castle into the portal, if you let them. Miniature Tower Defense is a tabletop game inspired by video games such as “Orcs Must Die” and “Sanctum” in which the hero places traps to stop mindless hordes of enemies, while also fighting them personally.