LPPT Lisbon

Hey guys. I have a project to make Lisbon airport on a scale of 1:500. My problem is if i just put the main buildings, both runways, cargo and maintenance buildings, it forms kind of a triangle (both runways cross each other). I guess that in this kind of models a rectangular or even a square shape is the ideal so im looking for some suggestions on how to build it as well as which materials to use.

I apologize if my english is not very good but i hope that you guys understand what i meant.