How to create a solid new body?

[Anonymous]

Hi, how to create a solid block over the top of this model without affecting what's underneath. So i just want a solid rectangular body that cover everything on top, but what's underneath is unaffected. 

[TheCADWhisperer]

I would use Extrude.

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?