  We introduce certain directed multigraphs with extra structure, called Weyl
graphs, which model quotients of Tits buildings by type-preserving chamber-free
group actions. Their advantage over complexes of groups, which are often used
for the CAT(0) Davis realization of buildings, is that Weyl graphs exploit the
ultimate combinatorial W-metric structure of buildings. Weyl graphs generalize
Tits's chambers systems of type M by allowing 2-residues to be quotients of
generalized polygons by flag-free group actions, and Weyl graphs are easily
constructed by amalgamating such quotients. We develop covering theory of Weyl
graphs, which can be used to construct buildings as universal covers. We
describe a method of obtaining a group presentation of the fundamental group of
a Weyl graph, which acts chamber-freely on the covering building. The theory
developed here is part of a fully general theory which deals with not
necessarily chamber-free actions and the stacky version of buildings.
