  Let T be a tile in the Cartesian plane made up of finitely many rectangles
whose corners have rational coordinates and whose sides are parallel to the
coordinate axes. This paper gives necessary and sufficient conditions for a
square to be tilable by finitely many \Q-weighted tiles with the same shape as
T, and necessary and sufficient conditions for a square to be tilable by
finitely many \Z-weighted tiles with the same shape as T. The main tool we use
is a variant of F. W. Barnes's algebraic theory of brick packing, which
converts tiling problems into problems in commutative algebra.
