Just to clarify all the above points
All existing buildings can be built outdoors on land or other in any other building type with the following exceptions
Lighthouses can only be built outside on land bordering water and only 1 per location is allowed
Coastal Harbours can only be built outside on land bordering sea (maximum number = 3 per location)
Landing Stages can only be built outside on land bordering lakes (up to 3 per location)
Stone Extensions can only be built indoors in halls,other stone extensions or buildings (essentially stone buildings)
Wood Extensions can only be built indoors in cottages or other wooden extensions
Cabins and cargo holds are reaching implementation - these will have construction limits - They will only be able to be built on the deck of specific types of boats and will be limited in number - So no cargo holds on rafts or cabins within cabins or 48 cabins on a raker.
When they are finalised full details,including any building restrictions, will be released here and the Wiki.