Need help to understand.

So my professor for my NetCom class just posted our homework for the week and I am totally confused on what he means about setting the network up in Packet Tracer.

These are the instructions/ requirements:

Use Packet Tracer to create the following Topology and attach to this question:

3 separate buildings using OSPF with the following guidelines:

Building A - 2 networks

Building B - 2 networks

Building C - 2 networks

Each building should have 1 layer 3 switch and 1 PC in each network.

Summarize the networks for each building as a class B summary in the routing tables.

Use areas to help with summarization

Label networking components (ip, subnet mask, gateway, default routes, routing tables, switch vlans, vlan IP’s, trunks, OSPF area’s)

Components allowed (3 Layer 3 Switches)

So i understand that i need to have the 3 layer 3 switches as the buildings. and then have 2 PCs coming off the layer 3 switch or have 2 more layer 3 switches coming off the first layer 3 switch. But i am only allowed 3 layer 3 switches so do i branch off the layer three switches with layer two switches? He confuses the hell out of me when he posts some homework sometimes. Once i get this topology set-up configuring OSPF for it should be a breeze. I have asked some other classmates( they are confused as well it seems) as well as emailing my professor, who has yet to respond. Thanks for the help.