Revit - How to Create a Model Fill Pattern

Revit can use any pat file to generate a model fill pattern with a slight tweak to the .pat file itself.

If you open the pattern file with notepad you will need to add the highlighted line below, and save the file with some designation so you know it's a model pattern.

Model Pattern Format

*Block 8x8, 8X8 block running bond
;%TYPE=MODEL
0, 0, 0, 0, 8
90, 0, 0, 8, 4, 8, -8

Fill Pattern Scale

The tricky part sometimes is getting the scale correct, so if you need to modify the scale you can reference this  blog.