@rubyskywalker Click on the lot in edit town hit save to library.Any other save you play the build will be there at the bottom with all other premade lots to place anywhere you like.You can also edit the lots name and give it a description there too
Bars pools parks etc you save will be under Community lots
Houses/Apartments you save will be residential
The other handy use of saving to library is good to do on long builds and you fear game may mess up whatever.
Hit save to library then rename it like "My build step one" and if your game crashed or froze or anything you will have last version saved to library to keep you from losing valuable work.After you finish a build simply trash the intermediate build saves.Really good to do if building or experimenting with the MOO cheat cause it can freeze your game it is very random can never happen or decide to right at the end of your awesome build.