Cloisters

From BoardGameGeek:

Cloisters is a simple but surprisingly deep two-player game, creating the look of a delightful complex of ancient cloisters as play progresses. Two players take it in turns to place one of the wooden blocks following a simple rule. As new cloisters are formed the monks switch their allegiance, and only a stonemason can make a new opening in the outer wall. The player with most monks at the end wins the game. -description from the publisher