This isn't really a GDL problem. It's more of a texturing problem so should probably be in the 'Presentation / Rendering' section.
There are (at least) 2 ways of doing this. It depends on whether the pattern is continually repeated, or the decorated tiles are a one-off feature in the middle of the floor.
If it does continually repeat, create a texture of a block of 3x3 plain tiles next to a block of patterned tiles. Save it in jpg/png format. Put it in a folder that has been loaded for use in archicad. Go into archicad and reload the libraries so the image becomes available for use. Go to materials and duplicate a similar existing one. Assign the image for use on that material, set the correct dimensions that you would expect the tiles to be. Set the colour and reflectivity etc. Click 'match with internal engine' in the lightworks settings so the texture shows in a render.
Assign that material to the slab. In the 3d window use the 'align 3D texture' tools to move and rotate it to the correct position.
An alternative would be to pre-set the rotation actually in the materials setting box, but you will still probably have to position it on the slab using align 3d texture.
The second option is more perhaps complicated if the areas of pattern are one-off features in the middle of the floor.
Create two textures, one of the plain tiles, and a separate one of the patterned. Save them as described before. In archicad create two new materials and assign a tile texture to each one. Set the size etc and 'match with internal' all as above.
With the slab tool, create one square area the same size as the pattern. Assign the pattern texture to it. Rotate it to 45 degrees. Use align 3d texture to position correctly. There should be no gaps or repetitions if the slab is the same size as the tile texture. Create another larger slab which will be the plain tiles, assign the the plain texture then align the texture. Duplicate and reposition the patterned tile slabs into the right places. Use SEO to subtract the patterned tiles from the plain tiles.
Finished! Hope that's clear enough!
For detailed help with creating materials and aligning textures, see the help files, and do a search on these forums for other posts.