The Iron Hand site has a tutorial on building a very nice building-sized laser defense battery for 25mm – 28mm science fiction games, such as Warhammer 40K. These would be great as the focal point of a scenario.
Olicanalad’s Games has an illustrated article on making Arab / Middle Eastern style buildings.
Terragenesis has an article on building an underground Jedi headquarters. It would work as a Hobbit house also.