Hi Nasma
DesignModeler has an default limit of 1 km 'bounding box' where are geometry has to be within this box. So that is +/- 500 m in each x/y/z direction. Which is why it fails to extrude more that 500 m in one direction.
In Tools -> Options; Units you can turn On the 'Large Model Support' which changes the bounding box to I think 10 km sides; 1000 km^3 total volume if I remember correctly.
Mike
You are navigating away from the AIS Discovery experience