One method disclosed herein involves, among other things, generating a set of mandrel mask rules, block mask rules and a virtual, software-based non-mandrel-metal mask. The method also includes creating a set of virtual non-mandrel mask rules that is a replica of the mandrel mask rules, generating a set of metal routing design rules based upon the mandrel mask rules, the block mask rules and the virtual non-mandrel mask rules, generating the circuit routing layout based upon the metal routing design rules, decomposing the circuit routing layout into a mandrel mask pattern and a block mask pattern, generating a first set of mask data corresponding to the mandrel mask pattern, and generating a second set of mask data corresponding to the block mask pattern.