As an early Eid gift (Eid will be on Sunday, inshallah), my Mom gave me Mosque by David Macaulay. It's an illustrated book that uses a fictional story to explain the architecture of Ottoman Turkish mosques. At first glance, it seems like a children's book but the actual level of the material is better suited for teenagers or at least older or highly gifted children. And adults will enjoy it too, inshallah.
Macaulay has written a whole series of these books, including ones about castles, cathedrals, ancient Roman cities and many other types of buildings. Architecture is something that has to be seen not just described in words so the illustrated book format is well suited to this type of book.
A couple of interesting looking sites on Islamic architecture are Islamic Arts and Architecture Organization and Islamic Architecture. A Google search turns up many more.
Some other posts at this site about Islamic architecture include The beauty of Islamic architecture, Lovely Islamic architecture, A picture, and a prayer, Mosques of New York City, and Islamic theory of art.