Young village by a river has acquired the patronage of a minor noble who wants to expand, partially by creating a defensible keep/center to which citizens could retreat in the event of an emergency/threat. Options include constructing a city wall from lumber from the nearby forest (offers stability in the sense that the defended location is the current city), or claiming and repairing some ruins about a mile away (farther to retreat, but more defensible with long-term staying power and might require less labor).
Phase 1: Choice
Forest
Must scout a suitable lumber-harvesting area. Random encounters with predators/monsters, then clear out a nest of [giant spiders?] to "resolve" area. Opportunity to ally with some fey or other forest denizens.
Ruined Keep
Dungeon delve. Clear out all the monsters/traps to secure the area. Find a bit of treasure in the process. Decentralized/nonlinear.
Phase 2: Progress
Finishing either project takes 20 days, plus 1d4 days for every 5 villagers killed. Every 10 days, merchants visit town.
Day 6 — Reports come in that livestock is disappearing during the night. Turns out a group of drakes has formed a nest on the far side of a hill across the river and is using the town as a hunting ground. Resolving this reveals the entrance to a dungeon (ancient temple?).
Day 21 — Foreigner starts recruiting townsfolk into an evil cult. Starting with 1 on Day 21, number of members doubles each day (2 on Day 22, 4 on Day 23, etc), but neutralized members don't count toward growth. First clue comes from Insight DC (18-X) that something's weird. Further investigation needed. Upon reaching a total of 50+ members, a secret base is established in a cave upstream and no further recruitment happens. Five days later, a ritual will be performed to augment the cult's elite with dark powers, and the following day they will assault the town with the intent to take it over.
Phase 3: Conclusion
Once the building project is completed, the patron moves into town. Promises economic boom. Turns out the noble wanted a remote location where nobody would notice he was facilitating arms deals with an ogre clan in the hills.