3d – How to get the cross-sectional area of a stl file in Matlab?

I need a help with this problem in Matlab.
I have a 3D scenario (.stl) and I would like to obtain the cross-sectional area by cutting this scenario with a horizontal plane. Finally, I would like to obtain an image with the area of the cross-section obtained. I need to solve this compulsorily in Matlab, not in other programs or using a CAD. Could anyone help me? Thanks in advance

f1 = stlread('scenario.stl');

patch('faces',f1.ConnectivityList,'vertices',f1.Points);