🙁 I grew up playing Sims 1 and Sims 2 where you can place lots anywhere you want to and really wish we had that in the Sims 4 with the newer build tools.
Its honestly really annoying to me that they filled the world with fake houses which look amazing and then there are like 3 lots to build on near them. Or place them on a lot next to the one you are working on in full size if that makes it easier to see. What you can do is find some of them in the debug cheat options – the cheat for the liveeditmode objects has some of the fake houses (not all of them I don’t think) and whilst they aren’t proper objects and can be walked through, you can place them on a lot sized down and use them as a reference to build something similar. They are just visual assets the sims team made to make the world look more populated whilst being able to run with very little resources (they were originally intending the game to be playable online with others and only at the very last minute did they realize that they couldn’t finish that idea in time which is why a lot of the game is very basic).