If you know where the vertices are, it should be fairly simple. Consider the very simplified example.
x = [0 10 10 0 0];
y = [0 0 10 10 0];
plot(x,y,'k'); hold on;
x = [0 2 2 4 4];
y = [6 6 8 8 10];
plot(x,y,'k:')
axis equal
xlim([-5 15])
ylim([-5 15])
Whether you explicitly define your vertices as literal vectors or whether you derive them from some CAD file shouldn't make much difference.
