Point(1) = {0, 0, 100, 30};
Point(2) = {0, 500, 100, 30};
Point(3) = {500, 500, 100, 30};
Point(4) = {500, 0, 100, 30};
Point(5) = {250, 500, 100, 30};
Point(6) = {250, 0, 100, 30};
Line(1) = {2,5};
Line(2) = {5,3};
Line(3) = {3,4};
Line(4) = {4,6};
Line(5) = {6,1};
Line(6) = {1,2};
Line(7) = {5,6};
Line Loop(8) = {7,-4,-3,-2};
Plane Surface(9) = {8};
Line Loop(10) = {6,1,7,5};
Plane Surface(11) = {10};

Recombine Surface {9};
Extrude {0,0,-100}{ 
  Surface{9}; Layers{10,1}; Recombine; 
}

Recombine Surface {11};
Extrude {0,0,-80}{ 
  Surface{11}; Layers{8,1}; Recombine; 
}
