Please look in to the tutorial attached
In top Plane draw a Centre Rectangle (square), and dimension it accordingly. I have given it a side of 200 mm
Select 3d Sketch, and then place a point approximately in center of the rectangle leaving some gap.
Dimension it from the center of square. it will be the height of the pyramid.
I have given a height of 150 mm.
Select the two sketch (Sketch1 and 3dsketch1) and select loft from features toolbar and click ok.