Here is the one I wrote in *.lsp format and it's based on Kent's Hatch Maker routine suggestion, but it may be a little buggy when complex hatches you want to create... If you have simple repeating pattern it's better than Hatch Maker in the way that you are not limited to draw lines inside boundary 100x100 units with snapping - boundary rectangle can be any size, but with greater scales it may fail to generate all you wish... You should select LINE entities inside and RECTANGULAR LWPOLYLINE that is serving as boundary for hatch repetitions... Yes, it's 100% free as I wrote it...
https://www.cadtutor.net/forum/topic/70417-make-pat-files/?do=findComment&comment=565434
HTH.
Marko Ribar, d.i.a. (graduated engineer of architecture)