Currently force building will fail on non-buildable tiles if you haven't placed a cover tile before on that specific non-buildable tile. This means that you need to first manually place a cover tile on every type of non-buildable tile before a force-build will work anywhere. It would be really great if the engine could make a guess as to what cover tile to use instead of failing. And failing can be frustrating to the player because it usually "just works".
An example (from here). Two different saves with the same conditions, but in one no cover tile has been placed before. Deciding which cover tile to use (when no default_cover_tile is set?) is a tricky question though that I don't have a good answer to. Could be for example
- Just the first coverable tile it finds. Possibly using the "order" field? Probably good enough regardless. If mod doesn't like it it should set the default_cover_tile.
- The cheapest tile in terms of raw resources. But would need to find the cheapest recipe to make that tile, which is also not really possible. What's cheaper, 5 stone or 5 iron?
- Something else?