Extrude command in 3d max , if you extruded walls not covered from the top from cad file , what would you do to complete extrude order correctly?

we can create any new command or change command in3ds max:

for example create extrude command: menu customize > customize user inter face >

All command underneath  

Example select extrude modifier then/ Hot Key: CTRL Press and hold +E than assign 

u sould try shell command else weld vertices then exturde

Check all vertices and weld it properly befor extrusion