Generally speaking, AutoCAD, Inventor, SolidWorks and other related engineering software works best on Windows machines. With that being said, I'll recommend:
ASUS Zenbook UX32VD Intel i7 3517U 6GB 500GB+24GB SSD GT620M 13.3in IPS FHD Win8 Ultrabook
or
ASUS N56VJ-RH71-CA Intel I7-3630QM 8GB 750GB 15.6in FHD GT635M DVDRW BT BANG&OLUFSEN Win8 Notebook
both similar in specs
For the zenbook, you might wanna upgrade the ram to at least 8GB