You can certainly do it using AFCAD but it limits your choices for grass textures a bit. If you use a program like SBuilder you can choose from about 80 different textures to use for the "airport grass".
SBuilder is a great program for creating airport background polygons but it takes a little while to learn to use. But once you understand it and understand the priority the MSFS uses to display different layers of scenery, you can make just about any kind of scenery you want.
SBuilder support forum is
here