Texturing - repeating pattern that won't distort when I resize object

I am trying to use procedural texture maps to make wallpaper in a model of a room.

I discovered that I could easily make a repeating pattern with procedural textures, but then if I resize the wall texture, the image distorts.

What can I do to make this work right? (i e have a pattern that stays the same size even when I expand the object)