What I do when importing cad to SU is do a save as and change all the linetypes to layer 0, make sure my model is on the 0,0 origin and then purge. Then do a LAYDEL command and delete any remaining layers. Make sure your drawing units are set up correctly otherwise it will come into SU not how you want it. In SU do a purge and group the floor plan. I never draw using the geometry from ACAD, it has always resulted in larger file sizes and corrupt drawings. Hope this helps.