Scott:
If you are referring to the texture, you can modify or create a Surface with any texture (bit map image), in the Help files see: User Interface Reference > Dialog Boxes > Surface Settings (CineRender) >
Surface Texture Panel (Internal Engine). Searching the internet will yield many textures for use.
If you are referring to the Vectorial Hatching, again you can create a custom Fill, in the Help file see: Documentation > Fills >
Create or Edit Symbol Fill.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David