A PATTERN LANGUAGE, by Christopher Alexander. Philosophy of
architecture. Other books by same author -- LINZ CAFE and TIMELESS WAY OF
LOOKING AROUND, by Witold Rybczynski. A collection of short essays
on a multitude of observations on architecture.
THE GOOD HOUSE; CONTRAST AS A DESIGN TOOL by authors Jacobson,
Silverstein and Winslow. Useful architectural design theory.
PLACES OF THE SOUL, by Christopher Day. Covers a broad scope of
ideas in architecture.
Hope this helps.