We consider weighted graphs with parameterized weights and we propose an algorithm that, given such a graph and a source node, builds a collection of trees, each one describing the shortest paths from the source to all the other nodes of the graph for a particular zone of the parameter space. Moreover, the union of these zones covers the full parameter space: given any valuation of the parameters, one of the trees gives the shortest paths from the source to all the other nodes of the graph when the weights are computed using this valuation.