Internal - Spiritual:
The rungs on a ladder represent levels in a hierarchy, and so can symbolise levels of spiritual awareness. A ladder may indicate communication between levels, or ascension to a higher spiritual plane.
Internal - Worldly:
Drawing doodles of ladders may indicate ambition and a desire to succeed, whether it is the corporate ladder you are climbing, or some other personal or professional goal. A firmly-drawn and regular ladder might suggest a firm resolve, while a shaky and uncertain ladder may indicate uncertainty. Got your ladder set against a wall? Perhaps you see obstacles in your way but you also have the means to surmount them.
External Sources:
Renovating? Ladder doodles might be inspired by their use somewhere in your environment, or possibly an experience with them in your past. Perhaps you own a ladder-back chair, or have played snakes-and-ladders lately?

