Aroka has the right idea, make it make sense, and take time to build up. Ultimately there has to be something there that people want, that could be trees from a forest, fertile land to grow food on or raise livestock, gold/silver/ other precious or useful metals, gems etc.


Also consider running an adventure where they have to take a “wagon train” to the desired destination


Really you don’t need any special rules for raising a town, just start small with a group of say ten settlers, and give PCs quests that will help their settlement grow.