Sounds like a great project.

You don't say what age group you are working with but I think these sources will help you.  You can modify them to the group to which you are working.  I would love to see the final result and process to share with others. 

How to Build a Topographic Model University of California (Berkeley)


National Geography Maps (Type in Poland)


Newton’s Apple


Topographic Map Unit Plan (High School Age Group)