This text is taken from a post by Dean Camlin. He describes how to change a pattern to a Model type pattern. (Refer to Revit HELP for an explanation of the differences between them)
A little supporting data clipped from Mr. Kendszersky's recent post...To convert any hatch pattern definition to a model pattern you need to add the line:
;%TYPE=MODEL
to the text file before the pattern definition. Then, Revit will recognize it as a model hatch.
In Revit, go to Settings > Fill Patterns ... Then, in the dialog box, select Model as the pattern type, select New, then Custom, then Import, and select the pattern file name (from wherever you have it stored) -- then, highlight the file name & play with the scale of the pattern, if necessary.
In Revit go to the settings pulldown, select fill patterns and then select the model radio button in the fill pattern dialogue box. Select new and enter a new model pattern name "Horiz. lines (Model)" you can edit line spacing, angle etc.
Once this is set, assign this new pattern to the material(s) surface pattern that you created. (Settings pulldown / Materials)
What is confusing is that revit does not distinguish between model / drafting patterns in the surface pattern pull down list when defining new materials. So the name that you give your pattern will help you distinguish one from another (model / drafting).