You need British Isles Stone forts for SS6 installed
http://www.twcenter.net/forums/showthread.php?t=163607
SCOTLAND buildable stone fort for for Stainless Steel 6
Unrar to SS6/data, including subfolders.
UNRAR optional rars to SS6/data for Custom models_strat (Inverness and stone fort) and fort/castles textures.
DOWNLOAD
http://files.filefront.com/scots+for.../fileinfo.html
(6.23 MB)
Enjoy!