StudioGo provides two best CAD designers available for Linux

GCAD 3D

3D-CAD/CAM-software with Iges-Import/Export, DXF-Import/Export, VRML-1, programming-Interface, scripting language.

Q-CAD

An application for computer aided drafting in two dimensions.

With QCad you can create technical drawings such as plans for buildings, interiors or mechanical parts