by Deroche
It depends on what you expect out of your maps: Massive, sprawling "free-builds", with huge point totals on both sides and a game that last for a few hours, or a typical skirmish battle on a pre-designed map that's intentionally balanced and fair, often found in a tournament setting, and the game plays in an hour or less (you can find lots of maps like these with build instructions over at heroscapers.com).
Either way is a legitimate way to play. The former will have you wishing for at least two sets, if not more. If the latter, then one set is usually sufficient.
Fortress sets often make for great road tile substitutes as well, which are only found in the Forest expansion. But maps that use road tiles more often than not use the trees that come with the Forest set as well. So, again, it depends on the map, etc.