06-09-2014, 06:11 PM
This will be possible with the new system. Until that you could have a look into the MeshHelper.CreateRectangle() method. It provides the shape used in the extrusion and ranges between -0.5 and 0.5 (that got multiplied with the width/height parameter in the extrusion). Just alter the vertices y value to range from -1 to 0 (or lower if you want more offset).