Hi,
This seams to be a simple task and can be done in 1hr - 2hr or less. All you need is a network with 20 nodes and few router(gateways) with different network, this topology can be designed and configured in both GNS and Cisco Packet Tracer, even in real world also.. within 1-2hrs..
I have more then 5 years of experience in this field.. I can do it with ease..