Writing bits in an array

Hi in my game i have a large array of structs containing landscape-tile and passabillity info. Now I have a lots of buildings, which can be rotated and placed on the map. A typical building migh be 6*10 tiles large. Now, when i place a building on the map in my game, i want to set the passabillity-bits to 1, even though the building might be rotated. Any1 got a clue how to do this fast ? I know i could go through each "tile" the building occupies and rotate it individually with sin-cos, but thats to slow for me. Anyone have another idea?