A few points that might help:
- Build limit: if you're at the build limit, your plot won't be able to build. If this is for a contest entry and you're at the limit I suggest you scrap some stuff and see if that helps. If you really want to you can disable this at the City Planner's Disk (or City Manager Holotape) in "Options -> Performance -> Respect Build Limit"
- Plot costs: your plot might not be building if some costs aren't met, you can disable that in "Options -> Gameplay -> Costs -> Construction Costs: Plot"
- Commercial requirement: your plot might need homes or a certain population to build. You can tweak that in "Options -> Gameplay -> Immersion -> Commercial Requirement"
- Build time: Plots need time to build, and will take even longer if you have "Options -> Gameplay -> Immersion -> Realistic Build Times" enabled
- Settler SPECIAL stats: If you have "Options -> Gameplay -> NPCs -> SPECIAL Stats Requirements" on, then only someone with enough stats for that plot will be eligible to build it.
- Auto assignment race conditions: Workshop Framework and SS2 might be "fighting" to auto-assign settlers to different stuff. I'd suggest disabling all auto assignment options in the Workshop Framework Controls holotape, "Options -> Assignment Options"
Edit: and some extra tips for troubleshooting, I just did this with some of my plots which still weren't building:
- Use the Asam's tracking feature to find out who's assigned to the plot. Maybe that settler is bugged or something
- If all else seems fine but the plot still won't build, try switching the building plan and it might start building!