I routinely do work for people based on their ideas and rough maps.

The licensing is CLEAR from the outset that in most cases this is not "work for hire" which means I have 100% copyright control over the finished product and am licensing it back to the person commissioning me for unlimited non-exclusive commercial and personal use, but that I also retain copyright and the ability to use and distribute the map.

This is an expected part of our negotiations and comes up a lot when people balk at my standard pricing for work-for-hire (which is about $300 for a black and white piece currently).