Which mods can I use?
You can only build with items from the following places: Sim Settlements 2, vanilla game objects, DLC objects, and objects from the mod Wasteland Reconstruction Kit.
Don't worry - you don't have to uninstall your other mods - we've thought of that! To help you keep track of what you can build - the City Plan Contest Assistant mod will automatically highlight anything that isn't legal in a glowing purple so you know instantly if you placed something you shouldn't have.
Recommended
Place Everywhere - This will allow you to place things in ways that would be very difficult otherwise.
Do NOT Use
Scrap Everything & Spring Cleaning - This mod will allow you to scrap much more than is possible for Sim Settlements to handle reliably and so won't work with City Plans in this contest If a mod lets you scrap something extra, you probably shouldn't use it.
All Settlements Extended & Annex the Commonwealth - Mods that increase the build area aren't necessarily a problem technically, like scrap mods are, but they will encourage a bad habit for this contest. If anyone using your City Plan doesn't have a border extending mod installed, the settlers who are assigned to items outside the vanilla build area will never be able to reach them.
What about Add-on Packs?
Yes and no. You can use Building Plans on your plots from any add-on you like! What you can't do, is build extra items from an add-on, for example, custom City Planner's Desks.
Building Plans are allowed because Sim Settlements 2 can dynamically change them for players not using the add-on you had, whereas it won't know how to handle the other items.