Importing the AutoCAD Drawings into 3DS Max

Before I started modelling the house, I needed to import the interior and exterior walls From AutoCAD to 3DS Max. To do this, I hid all of the details aside from the walls in the top view (images 1 and 2) and then saved the file as a new file and opened 3DS Max. After opening 3DS Max, I went to file then down to import then clicked on import and found the new I made sure that all the vertices where welded together so that when I applied the extrude modifier to the splines, the top would be capped (as seen in image 4) rather than open at the top.