Room deactivation is an effect brought on by the Spell card Freeze. Once deactivated the Room will automatically reactivate in the End of Turn Phase, it cannot be reactivated manually. A deactivated Room counts as a empty Room with no damage, Treasure, or Effects.
Any cards next to the deactivated Room with an effect on adjacent cards does effect the deactivated Room and does not pass over the deactivated Room. Rooms cannot be built ontop of a currently deactivated Room. Deactivated Rooms cannot be destroyed until they are reactivated.
Reasons to deactivate your own RoomEdit
1) In the Build Phase a player may not want to draw in certain Heroes. For example, lets say an Epic Fighter had 15 HP, but the players Dungeon can only do 12 damage and they have no Spells or Effects to increase this. The player could deactivate a Fighter Room in order to lower their treasure count and keep from taking two Wounds.
Note: Since a Room deactivated in the Build Phase will also be deactivated in the Adventure Phase that means any damage or special effects the Room might have will also be disable. In all likelihood this will decrease the total damage the Dungeon can use so it should be used carefully.
2) In the Adventure Phase a player could deactivate a Room in order to make sure a Hero dies in a specific Room. This could be to the players advantage since some Rooms have special effects based on if a Hero dies in that specific Room.
This method has far less risk since the Room will be reactivated once the Adventure Phase ends.